restore mistakenly removed iffs in their explicit formrefs/pull/2387/head

Due to confusion arisen from "iff" standing for "if and only if",
this commit uses the latter.

22 files changed, 223 insertions, 211 deletions

diff --git a/googletest/include/gtest/gtest-death-test.h b/googletest/include/gtest/gtest-death-test.h
index cec9629..dc878ff 100644
--- a/googletest/include/gtest/gtest-death-test.h
+++ b/googletest/include/gtest/gtest-death-test.h
@@ -276,20 +276,20 @@ class GTEST_API_ KilledBySignal {
 // This macro is used for implementing macros such as
 // EXPECT_DEATH_IF_SUPPORTED and ASSERT_DEATH_IF_SUPPORTED on systems where
 // death tests are not supported. Those macros must compile on such systems
-// if EXPECT_DEATH and ASSERT_DEATH compile with the same parameters on
-// systems that support death tests. This allows one to write such a macro
-// on a system that does not support death tests and be sure that it will
-// compile on a death-test supporting system. It is exposed publicly so that
-// systems that have death-tests with stricter requirements than
-// GTEST_HAS_DEATH_TEST can write their own equivalent of
-// EXPECT_DEATH_IF_SUPPORTED and ASSERT_DEATH_IF_SUPPORTED.
+// if and only if EXPECT_DEATH and ASSERT_DEATH compile with the same parameters
+// on systems that support death tests. This allows one to write such a macro on
+// a system that does not support death tests and be sure that it will compile
+// on a death-test supporting system. It is exposed publicly so that systems
+// that have death-tests with stricter requirements than GTEST_HAS_DEATH_TEST
+// can write their own equivalent of EXPECT_DEATH_IF_SUPPORTED and
+// ASSERT_DEATH_IF_SUPPORTED.
 //
 // Parameters:
 //   statement -  A statement that a macro such as EXPECT_DEATH would test
 //                for program termination. This macro has to make sure this
 //                statement is compiled but not executed, to ensure that
 //                EXPECT_DEATH_IF_SUPPORTED compiles with a certain
-//                parameter if EXPECT_DEATH compiles with it.
+//                parameter if and only if EXPECT_DEATH compiles with it.
 //   regex     -  A regex that a macro such as EXPECT_DEATH would use to test
 //                the output of statement.  This parameter has to be
 //                compiled but not evaluated by this macro, to ensure that
diff --git a/googletest/include/gtest/gtest-matchers.h b/googletest/include/gtest/gtest-matchers.h
index 0548806..187c290 100644
--- a/googletest/include/gtest/gtest-matchers.h
+++ b/googletest/include/gtest/gtest-matchers.h
@@ -96,8 +96,8 @@ class MatchResultListener {
   // Returns the underlying ostream.
   ::std::ostream* stream() { return stream_; }
 
-  // Returns true if the listener is interested in an explanation of
-  // the match result.  A matcher's MatchAndExplain() method can use
+  // Returns true if and only if the listener is interested in an explanation
+  // of the match result.  A matcher's MatchAndExplain() method can use
   // this information to avoid generating the explanation when no one
   // intends to hear it.
   bool IsInterested() const { return stream_ != nullptr; }
@@ -141,8 +141,8 @@ class MatcherDescriberInterface {
 template <typename T>
 class MatcherInterface : public MatcherDescriberInterface {
  public:
-  // Returns true if the matcher matches x; also explains the match
-  // result to 'listener' if necessary (see the next paragraph), in
+  // Returns true if and only if the matcher matches x; also explains the
+  // match result to 'listener' if necessary (see the next paragraph), in
   // the form of a non-restrictive relative clause ("which ...",
   // "whose ...", etc) that describes x.  For example, the
   // MatchAndExplain() method of the Pointee(...) matcher should
@@ -258,13 +258,13 @@ class StreamMatchResultListener : public MatchResultListener {
 template <typename T>
 class MatcherBase {
  public:
-  // Returns true if the matcher matches x; also explains the match
-  // result to 'listener'.
+  // Returns true if and only if the matcher matches x; also explains the
+  // match result to 'listener'.
   bool MatchAndExplain(const T& x, MatchResultListener* listener) const {
     return impl_->MatchAndExplain(x, listener);
   }
 
-  // Returns true if this matcher matches x.
+  // Returns true if and only if this matcher matches x.
   bool Matches(const T& x) const {
     DummyMatchResultListener dummy;
     return MatchAndExplain(x, &dummy);
diff --git a/googletest/include/gtest/gtest-test-part.h b/googletest/include/gtest/gtest-test-part.h
index 4f189b6..05a7985 100644
--- a/googletest/include/gtest/gtest-test-part.h
+++ b/googletest/include/gtest/gtest-test-part.h
@@ -87,19 +87,19 @@ class GTEST_API_ TestPartResult {
   // Gets the message associated with the test part.
   const char* message() const { return message_.c_str(); }
 
-  // Returns true if the test part was skipped.
+  // Returns true if and only if the test part was skipped.
   bool skipped() const { return type_ == kSkip; }
 
-  // Returns true if the test part passed.
+  // Returns true if and only if the test part passed.
   bool passed() const { return type_ == kSuccess; }
 
-  // Returns true if the test part non-fatally failed.
+  // Returns true if and only if the test part non-fatally failed.
   bool nonfatally_failed() const { return type_ == kNonFatalFailure; }
 
-  // Returns true if the test part fatally failed.
+  // Returns true if and only if the test part fatally failed.
   bool fatally_failed() const { return type_ == kFatalFailure; }
 
-  // Returns true if the test part failed.
+  // Returns true if and only if the test part failed.
   bool failed() const { return fatally_failed() || nonfatally_failed(); }
 
  private:
diff --git a/googletest/include/gtest/gtest.h b/googletest/include/gtest/gtest.h
index db81359..98c1949 100644
--- a/googletest/include/gtest/gtest.h
+++ b/googletest/include/gtest/gtest.h
@@ -308,7 +308,7 @@ class GTEST_API_ AssertionResult {
     return *this;
   }
 
-  // Returns true if the assertion succeeded.
+  // Returns true if and only if the assertion succeeded.
   operator bool() const { return success_; }  // NOLINT
 
   // Returns the assertion's negation. Used with EXPECT/ASSERT_FALSE.
@@ -432,16 +432,16 @@ class GTEST_API_ Test {
   static void SetUpTestCase() {}
 #endif  // GTEST_REMOVE_LEGACY_TEST_CASEAPI_
 
-  // Returns true if the current test has a fatal failure.
+  // Returns true if and only if the current test has a fatal failure.
   static bool HasFatalFailure();
 
-  // Returns true if the current test has a non-fatal failure.
+  // Returns true if and only if the current test has a non-fatal failure.
   static bool HasNonfatalFailure();
 
-  // Returns true if the current test was skipped.
+  // Returns true if and only if the current test was skipped.
   static bool IsSkipped();
 
-  // Returns true if the current test has a (either fatal or
+  // Returns true if and only if the current test has a (either fatal or
   // non-fatal) failure.
   static bool HasFailure() { return HasFatalFailure() || HasNonfatalFailure(); }
 
@@ -472,8 +472,8 @@ class GTEST_API_ Test {
   virtual void TearDown();
 
  private:
-  // Returns true if the current test has the same fixture class as
-  // the first test in the current test suite.
+  // Returns true if and only if the current test has the same fixture class
+  // as the first test in the current test suite.
   static bool HasSameFixtureClass();
 
   // Runs the test after the test fixture has been set up.
@@ -574,19 +574,19 @@ class GTEST_API_ TestResult {
   // Returns the number of the test properties.
   int test_property_count() const;
 
-  // Returns true if the test passed (i.e. no test part failed).
+  // Returns true if and only if the test passed (i.e. no test part failed).
   bool Passed() const { return !Skipped() && !Failed(); }
 
-  // Returns true if the test was skipped.
+  // Returns true if and only if the test was skipped.
   bool Skipped() const;
 
-  // Returns true if the test failed.
+  // Returns true if and only if the test failed.
   bool Failed() const;
 
-  // Returns true if the test fatally failed.
+  // Returns true if and only if the test fatally failed.
   bool HasFatalFailure() const;
 
-  // Returns true if the test has a non-fatal failure.
+  // Returns true if and only if the test has a non-fatal failure.
   bool HasNonfatalFailure() const;
 
   // Returns the elapsed time, in milliseconds.
@@ -750,7 +750,7 @@ class GTEST_API_ TestInfo {
   // contains the character 'A' or starts with "Foo.".
   bool should_run() const { return should_run_; }
 
-  // Returns true if this test will appear in the XML report.
+  // Returns true if and only if this test will appear in the XML report.
   bool is_reportable() const {
     // The XML report includes tests matching the filter, excluding those
     // run in other shards.
@@ -808,12 +808,12 @@ class GTEST_API_ TestInfo {
   // value-parameterized test.
   const std::unique_ptr<const ::std::string> value_param_;
   internal::CodeLocation location_;
-  const internal::TypeId fixture_class_id_;   // ID of the test fixture class
-  bool should_run_;                 // True if this test should run
-  bool is_disabled_;                // True if this test is disabled
-  bool matches_filter_;             // True if this test matches the
-                                    // user-specified filter.
-  bool is_in_another_shard_;        // Will be run in another shard.
+  const internal::TypeId fixture_class_id_;  // ID of the test fixture class
+  bool should_run_;           // True if and only if this test should run
+  bool is_disabled_;          // True if and only if this test is disabled
+  bool matches_filter_;       // True if this test matches the
+                              // user-specified filter.
+  bool is_in_another_shard_;  // Will be run in another shard.
   internal::TestFactoryBase* const factory_;  // The factory that creates
                                               // the test object
 
@@ -885,10 +885,10 @@ class GTEST_API_ TestSuite {
   // Gets the number of all tests in this test suite.
   int total_test_count() const;
 
-  // Returns true if the test suite passed.
+  // Returns true if and only if the test suite passed.
   bool Passed() const { return !Failed(); }
 
-  // Returns true if the test suite failed.
+  // Returns true if and only if the test suite failed.
   bool Failed() const { return failed_test_count() > 0; }
 
   // Returns the elapsed time, in milliseconds.
@@ -956,33 +956,33 @@ class GTEST_API_ TestSuite {
     }
   }
 
-  // Returns true if test passed.
+  // Returns true if and only if test passed.
   static bool TestPassed(const TestInfo* test_info) {
     return test_info->should_run() && test_info->result()->Passed();
   }
 
-  // Returns true if test skipped.
+  // Returns true if and only if test skipped.
   static bool TestSkipped(const TestInfo* test_info) {
     return test_info->should_run() && test_info->result()->Skipped();
   }
 
-  // Returns true if test failed.
+  // Returns true if and only if test failed.
   static bool TestFailed(const TestInfo* test_info) {
     return test_info->should_run() && test_info->result()->Failed();
   }
 
-  // Returns true if the test is disabled and will be reported in the XML
-  // report.
+  // Returns true if and only if the test is disabled and will be reported in
+  // the XML report.
   static bool TestReportableDisabled(const TestInfo* test_info) {
     return test_info->is_reportable() && test_info->is_disabled_;
   }
 
-  // Returns true if test is disabled.
+  // Returns true if and only if test is disabled.
   static bool TestDisabled(const TestInfo* test_info) {
     return test_info->is_disabled_;
   }
 
-  // Returns true if this test will appear in the XML report.
+  // Returns true if and only if this test will appear in the XML report.
   static bool TestReportable(const TestInfo* test_info) {
     return test_info->is_reportable();
   }
@@ -1014,7 +1014,7 @@ class GTEST_API_ TestSuite {
   internal::SetUpTestSuiteFunc set_up_tc_;
   // Pointer to the function that tears down the test suite.
   internal::TearDownTestSuiteFunc tear_down_tc_;
-  // True if any test in this test suite should run.
+  // True if and only if any test in this test suite should run.
   bool should_run_;
   // The start time, in milliseconds since UNIX Epoch.
   TimeInMillis start_timestamp_;
@@ -1349,11 +1349,12 @@ class GTEST_API_ UnitTest {
   // Gets the elapsed time, in milliseconds.
   TimeInMillis elapsed_time() const;
 
-  // Returns true if the unit test passed (i.e. all test suites passed).
+  // Returns true if and only if the unit test passed (i.e. all test suites
+  // passed).
   bool Passed() const;
 
-  // Returns true if the unit test failed (i.e. some test suite failed
-  // or something outside of all tests failed).
+  // Returns true if and only if the unit test failed (i.e. some test suite
+  // failed or something outside of all tests failed).
   bool Failed() const;
 
   // Gets the i-th test suite among all the test suites. i can range from 0 to
@@ -2267,8 +2268,8 @@ class GTEST_API_ ScopedTrace {
 
 
 // Compile-time assertion for type equality.
-// StaticAssertTypeEq<type1, type2>() compiles if type1 and type2 are
-// the same type.  The value it returns is not interesting.
+// StaticAssertTypeEq<type1, type2>() compiles if and only if type1 and type2
+// are the same type.  The value it returns is not interesting.
 //
 // Instead of making StaticAssertTypeEq a class template, we make it a
 // function template that invokes a helper class template.  This
diff --git a/googletest/include/gtest/internal/gtest-filepath.h b/googletest/include/gtest/internal/gtest-filepath.h
index 5d21bbc..c11b101 100644
--- a/googletest/include/gtest/internal/gtest-filepath.h
+++ b/googletest/include/gtest/internal/gtest-filepath.h
@@ -110,7 +110,7 @@ class GTEST_API_ FilePath {
                                          const FilePath& base_name,
                                          const char* extension);
 
-  // Returns true if the path is "".
+  // Returns true if and only if the path is "".
   bool IsEmpty() const { return pathname_.empty(); }
 
   // If input name has a trailing separator character, removes it and returns
diff --git a/googletest/include/gtest/internal/gtest-internal.h b/googletest/include/gtest/internal/gtest-internal.h
index 240d791..c3cf727 100644
--- a/googletest/include/gtest/internal/gtest-internal.h
+++ b/googletest/include/gtest/internal/gtest-internal.h
@@ -189,7 +189,7 @@ GTEST_API_ std::string DiffStrings(const std::string& left,
 //   expected_value:      "5"
 //   actual_value:        "6"
 //
-// The ignoring_case parameter is true if the assertion is a
+// The ignoring_case parameter is true if and only if the assertion is a
 // *_STRCASEEQ*.  When it's true, the string " (ignoring case)" will
 // be inserted into the message.
 GTEST_API_ AssertionResult EqFailure(const char* expected_expression,
@@ -318,15 +318,15 @@ class FloatingPoint {
   // Returns the sign bit of this number.
   Bits sign_bit() const { return kSignBitMask & u_.bits_; }
 
-  // Returns true if this is NAN (not a number).
+  // Returns true if and only if this is NAN (not a number).
   bool is_nan() const {
     // It's a NAN if the exponent bits are all ones and the fraction
     // bits are not entirely zeros.
     return (exponent_bits() == kExponentBitMask) && (fraction_bits() != 0);
   }
 
-  // Returns true if this number is at most kMaxUlps ULP's away from
-  // rhs.  In particular, this function:
+  // Returns true if and only if this number is at most kMaxUlps ULP's away
+  // from rhs.  In particular, this function:
   //
   //   - returns false if either number is (or both are) NAN.
   //   - treats really large numbers as almost equal to infinity.
@@ -848,7 +848,7 @@ class GTEST_API_ Random {
 };
 
 // Defining a variable of type CompileAssertTypesEqual<T1, T2> will cause a
-// compiler error if T1 and T2 are different types.
+// compiler error if and only if T1 and T2 are different types.
 template <typename T1, typename T2>
 struct CompileAssertTypesEqual;
 
@@ -895,7 +895,7 @@ struct RemoveConst<const T[N]> {
     GTEST_REMOVE_CONST_(GTEST_REMOVE_REFERENCE_(T))
 
 // IsAProtocolMessage<T>::value is a compile-time bool constant that's
-// true if T is type proto2::Message or a subclass of it.
+// true if and only if T is type proto2::Message or a subclass of it.
 template <typename T>
 struct IsAProtocolMessage
     : public bool_constant<
diff --git a/googletest/include/gtest/internal/gtest-port.h b/googletest/include/gtest/internal/gtest-port.h
index 7f00fe7..18dd637 100644
--- a/googletest/include/gtest/internal/gtest-port.h
+++ b/googletest/include/gtest/internal/gtest-port.h
@@ -362,7 +362,8 @@ typedef struct _RTL_CRITICAL_SECTION GTEST_CRITICAL_SECTION;
 #  include <android/api-level.h>  // NOLINT
 #endif
 
-// Defines this to true if Google Test can use POSIX regular expressions.
+// Defines this to true if and only if Google Test can use POSIX regular
+// expressions.
 #ifndef GTEST_HAS_POSIX_RE
 # if GTEST_OS_LINUX_ANDROID
 // On Android, <regex.h> is only available starting with Gingerbread.
@@ -403,7 +404,7 @@ typedef struct _RTL_CRITICAL_SECTION GTEST_CRITICAL_SECTION;
 // The user didn't tell us whether exceptions are enabled, so we need
 // to figure it out.
 # if defined(_MSC_VER) && defined(_CPPUNWIND)
-// MSVC defines _CPPUNWIND to 1 if exceptions are enabled.
+// MSVC defines _CPPUNWIND to 1 if and only if exceptions are enabled.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__BORLANDC__)
 // C++Builder's implementation of the STL uses the _HAS_EXCEPTIONS
@@ -414,16 +415,17 @@ typedef struct _RTL_CRITICAL_SECTION GTEST_CRITICAL_SECTION;
 #  endif  // _HAS_EXCEPTIONS
 #  define GTEST_HAS_EXCEPTIONS _HAS_EXCEPTIONS
 # elif defined(__clang__)
-// clang defines __EXCEPTIONS if exceptions are enabled before clang 220714,
-// but if cleanups are enabled after that. In Obj-C++ files, there can be
-// cleanups for ObjC exceptions which also need cleanups, even if C++ exceptions
-// are disabled. clang has __has_feature(cxx_exceptions) which checks for C++
-// exceptions starting at clang r206352, but which checked for cleanups prior to
-// that. To reliably check for C++ exception availability with clang, check for
+// clang defines __EXCEPTIONS if and only if exceptions are enabled before clang
+// 220714, but if and only if cleanups are enabled after that. In Obj-C++ files,
+// there can be cleanups for ObjC exceptions which also need cleanups, even if
+// C++ exceptions are disabled. clang has __has_feature(cxx_exceptions) which
+// checks for C++ exceptions starting at clang r206352, but which checked for
+// cleanups prior to that. To reliably check for C++ exception availability with
+// clang, check for
 // __EXCEPTIONS && __has_feature(cxx_exceptions).
 #  define GTEST_HAS_EXCEPTIONS (__EXCEPTIONS && __has_feature(cxx_exceptions))
 # elif defined(__GNUC__) && __EXCEPTIONS
-// gcc defines __EXCEPTIONS to 1 if exceptions are enabled.
+// gcc defines __EXCEPTIONS to 1 if and only if exceptions are enabled.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__SUNPRO_CC)
 // Sun Pro CC supports exceptions.  However, there is no compile-time way of
@@ -431,7 +433,7 @@ typedef struct _RTL_CRITICAL_SECTION GTEST_CRITICAL_SECTION;
 // they are enabled unless the user tells us otherwise.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__IBMCPP__) && __EXCEPTIONS
-// xlC defines __EXCEPTIONS to 1 if exceptions are enabled.
+// xlC defines __EXCEPTIONS to 1 if and only if exceptions are enabled.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__HP_aCC)
 // Exception handling is in effect by default in HP aCC compiler. It has to
@@ -472,13 +474,14 @@ typedef struct _RTL_CRITICAL_SECTION GTEST_CRITICAL_SECTION;
 
 # ifdef _MSC_VER
 
-#  ifdef _CPPRTTI  // MSVC defines this macro if RTTI is enabled.
+#  ifdef _CPPRTTI  // MSVC defines this macro if and only if RTTI is enabled.
 #   define GTEST_HAS_RTTI 1
 #  else
 #   define GTEST_HAS_RTTI 0
 #  endif
 
-// Starting with version 4.3.2, gcc defines __GXX_RTTI if RTTI is enabled.
+// Starting with version 4.3.2, gcc defines __GXX_RTTI if and only if RTTI is
+// enabled.
 # elif defined(__GNUC__)
 
 #  ifdef __GXX_RTTI
@@ -899,9 +902,9 @@ class GTEST_API_ RE {
   // Returns the string representation of the regex.
   const char* pattern() const { return pattern_; }
 
-  // FullMatch(str, re) returns true if regular expression re matches
-  // the entire str.
-  // PartialMatch(str, re) returns true if regular expression re
+  // FullMatch(str, re) returns true if and only if regular expression re
+  // matches the entire str.
+  // PartialMatch(str, re) returns true if and only if regular expression re
   // matches a substring of str (including str itself).
   static bool FullMatch(const ::std::string& str, const RE& re) {
     return FullMatch(str.c_str(), re);
@@ -1256,7 +1259,8 @@ class GTEST_API_ AutoHandle {
   void Reset(Handle handle);
 
  private:
-  // Returns true if the handle is a valid handle object that can be closed.
+  // Returns true if and only if the handle is a valid handle object that can be
+  // closed.
   bool IsCloseable() const;
 
   Handle handle_;
@@ -1358,7 +1362,8 @@ class ThreadWithParam : public ThreadWithParamBase {
   // When non-NULL, used to block execution until the controller thread
   // notifies.
   Notification* const thread_can_start_;
-  bool finished_;  // true if we know that the thread function has finished.
+  bool finished_;  // true if and only if we know that the thread function has
+                   // finished.
   pthread_t thread_;  // The native thread object.
 
   GTEST_DISALLOW_COPY_AND_ASSIGN_(ThreadWithParam);
diff --git a/googletest/include/gtest/internal/gtest-string.h b/googletest/include/gtest/internal/gtest-string.h
index 26d8407..82aaa63 100644
--- a/googletest/include/gtest/internal/gtest-string.h
+++ b/googletest/include/gtest/internal/gtest-string.h
@@ -94,7 +94,8 @@ class GTEST_API_ String {
   static const char* Utf16ToAnsi(LPCWSTR utf16_str);
 #endif
 
-  // Compares two C strings.  Returns true if they have the same content.
+  // Compares two C strings.  Returns true if and only if they have the same
+  // content.
   //
   // Unlike strcmp(), this function can handle NULL argument(s).  A
   // NULL C string is considered different to any non-NULL C string,
@@ -107,16 +108,16 @@ class GTEST_API_ String {
   // returned.
   static std::string ShowWideCString(const wchar_t* wide_c_str);
 
-  // Compares two wide C strings.  Returns true if they have the same
-  // content.
+  // Compares two wide C strings.  Returns true if and only if they have the
+  // same content.
   //
   // Unlike wcscmp(), this function can handle NULL argument(s).  A
   // NULL C string is considered different to any non-NULL C string,
   // including the empty string.
   static bool WideCStringEquals(const wchar_t* lhs, const wchar_t* rhs);
 
-  // Compares two C strings, ignoring case.  Returns true if they
-  // have the same content.
+  // Compares two C strings, ignoring case.  Returns true if and only if
+  // they have the same content.
   //
   // Unlike strcasecmp(), this function can handle NULL argument(s).
   // A NULL C string is considered different to any non-NULL C string,
@@ -124,8 +125,8 @@ class GTEST_API_ String {
   static bool CaseInsensitiveCStringEquals(const char* lhs,
                                            const char* rhs);
 
-  // Compares two wide C strings, ignoring case.  Returns true if they
-  // have the same content.
+  // Compares two wide C strings, ignoring case.  Returns true if and only if
+  // they have the same content.
   //
   // Unlike wcscasecmp(), this function can handle NULL argument(s).
   // A NULL C string is considered different to any non-NULL wide C string,
@@ -139,8 +140,8 @@ class GTEST_API_ String {
   static bool CaseInsensitiveWideCStringEquals(const wchar_t* lhs,
                                                const wchar_t* rhs);
 
-  // Returns true if the given string ends with the given suffix, ignoring
-  // case. Any string is considered to end with an empty suffix.
+  // Returns true if and only if the given string ends with the given suffix,
+  // ignoring case. Any string is considered to end with an empty suffix.
   static bool EndsWithCaseInsensitive(
       const std::string& str, const std::string& suffix);
 
diff --git a/googletest/samples/prime_tables.h b/googletest/samples/prime_tables.h
index 4178e70..72539bf 100644
--- a/googletest/samples/prime_tables.h
+++ b/googletest/samples/prime_tables.h
@@ -43,7 +43,7 @@ class PrimeTable {
  public:
   virtual ~PrimeTable() {}
 
-  // Returns true if n is a prime number.
+  // Returns true if and only if n is a prime number.
   virtual bool IsPrime(int n) const = 0;
 
   // Returns the smallest prime number greater than p; or returns -1
diff --git a/googletest/samples/sample1.cc b/googletest/samples/sample1.cc
index 58dbf17..1d42759 100644
--- a/googletest/samples/sample1.cc
+++ b/googletest/samples/sample1.cc
@@ -41,7 +41,7 @@ int Factorial(int n) {
   return result;
 }
 
-// Returns true if n is a prime number.
+// Returns true if and only if n is a prime number.
 bool IsPrime(int n) {
   // Trivial case 1: small numbers
   if (n <= 1) return false;
diff --git a/googletest/samples/sample1.h b/googletest/samples/sample1.h
index a90eae4..12e49de 100644
--- a/googletest/samples/sample1.h
+++ b/googletest/samples/sample1.h
@@ -35,7 +35,7 @@
 // Returns n! (the factorial of n).  For negative n, n! is defined to be 1.
 int Factorial(int n);
 
-// Returns true if n is a prime number.
+// Returns true if and only if n is a prime number.
 bool IsPrime(int n);
 
 #endif  // GTEST_SAMPLES_SAMPLE1_H_
diff --git a/googletest/src/gtest-death-test.cc b/googletest/src/gtest-death-test.cc
index e5ec287..da09a1c 100644
--- a/googletest/src/gtest-death-test.cc
+++ b/googletest/src/gtest-death-test.cc
@@ -122,8 +122,8 @@ GTEST_DEFINE_string_(
     "Indicates the file, line number, temporal index of "
     "the single death test to run, and a file descriptor to "
     "which a success code may be sent, all separated by "
-    "the '|' characters.  This flag is specified if and only if the current "
-    "process is a sub-process launched for running a thread-safe "
+    "the '|' characters.  This flag is specified if and only if the "
+    "current process is a sub-process launched for running a thread-safe "
     "death test.  FOR INTERNAL USE ONLY.");
 }  // namespace internal
 
@@ -563,8 +563,8 @@ static ::std::string FormatDeathTestOutput(const ::std::string& output) {
 //   status_ok: true if exit_status is acceptable in the context of
 //              this particular death test, which fails if it is false
 //
-// Returns true if all of the above conditions are met.  Otherwise, the
-// first failing condition, in the order given above, is the one that is
+// Returns true if and only if all of the above conditions are met.  Otherwise,
+// the first failing condition, in the order given above, is the one that is
 // reported. Also sets the last death test message string.
 bool DeathTestImpl::Passed(bool status_ok) {
   if (!spawned())
diff --git a/googletest/src/gtest-internal-inl.h b/googletest/src/gtest-internal-inl.h
index e29d992..8ed70da 100644
--- a/googletest/src/gtest-internal-inl.h
+++ b/googletest/src/gtest-internal-inl.h
@@ -99,14 +99,14 @@ const char kFlagfileFlag[] = "flagfile";
 // A valid random seed must be in [1, kMaxRandomSeed].
 const int kMaxRandomSeed = 99999;
 
-// g_help_flag is true if the --help flag or an equivalent form is
-// specified on the command line.
+// g_help_flag is true if and only if the --help flag or an equivalent form
+// is specified on the command line.
 GTEST_API_ extern bool g_help_flag;
 
 // Returns the current time in milliseconds.
 GTEST_API_ TimeInMillis GetTimeInMillis();
 
-// Returns true if Google Test should use colors in the output.
+// Returns true if and only if Google Test should use colors in the output.
 GTEST_API_ bool ShouldUseColor(bool stdout_is_tty);
 
 // Formats the given time in milliseconds as seconds.
@@ -266,8 +266,8 @@ GTEST_API_ bool ShouldShard(const char* total_shards_str,
 GTEST_API_ Int32 Int32FromEnvOrDie(const char* env_var, Int32 default_val);
 
 // Given the total number of shards, the shard index, and the test id,
-// returns true if the test should be run on this shard. The test id is
-// some arbitrary but unique non-negative integer assigned to each test
+// returns true if and only if the test should be run on this shard. The test id
+// is some arbitrary but unique non-negative integer assigned to each test
 // method. Assumes that 0 <= shard_index < total_shards.
 GTEST_API_ bool ShouldRunTestOnShard(
     int total_shards, int shard_index, int test_id);
@@ -352,7 +352,7 @@ class TestPropertyKeyIs {
   // TestPropertyKeyIs has NO default constructor.
   explicit TestPropertyKeyIs(const std::string& key) : key_(key) {}
 
-  // Returns true if the test name of test property matches on key_.
+  // Returns true if and only if the test name of test property matches on key_.
   bool operator()(const TestProperty& test_property) const {
     return test_property.key() == key_;
   }
@@ -385,15 +385,15 @@ class GTEST_API_ UnitTestOptions {
 
   // Functions for processing the gtest_filter flag.
 
-  // Returns true if the wildcard pattern matches the string.  The
-  // first ':' or '\0' character in pattern marks the end of it.
+  // Returns true if and only if the wildcard pattern matches the string.
+  // The first ':' or '\0' character in pattern marks the end of it.
   //
   // This recursive algorithm isn't very efficient, but is clear and
   // works well enough for matching test names, which are short.
   static bool PatternMatchesString(const char *pattern, const char *str);
 
-  // Returns true if the user-specified filter matches the test suite
-  // name and the test name.
+  // Returns true if and only if the user-specified filter matches the test
+  // suite name and the test name.
   static bool FilterMatchesTest(const std::string& test_suite_name,
                                 const std::string& test_name);
 
@@ -577,11 +577,12 @@ class GTEST_API_ UnitTestImpl {
   // Gets the elapsed time, in milliseconds.
   TimeInMillis elapsed_time() const { return elapsed_time_; }
 
-  // Returns true if the unit test passed (i.e. all test suites passed).
+  // Returns true if and only if the unit test passed (i.e. all test suites
+  // passed).
   bool Passed() const { return !Failed(); }
 
-  // Returns true if the unit test failed (i.e. some test suite failed
-  // or something outside of all tests failed).
+  // Returns true if and only if the unit test failed (i.e. some test suite
+  // failed or something outside of all tests failed).
   bool Failed() const {
     return failed_test_suite_count() > 0 || ad_hoc_test_result()->Failed();
   }
@@ -911,7 +912,7 @@ class GTEST_API_ UnitTestImpl {
   // desired.
   OsStackTraceGetterInterface* os_stack_trace_getter_;
 
-  // True if PostFlagParsingInit() has been called.
+  // True if and only if PostFlagParsingInit() has been called.
   bool post_flag_parse_init_performed_;
 
   // The random number seed used at the beginning of the test run.
diff --git a/googletest/src/gtest-port.cc b/googletest/src/gtest-port.cc
index 9024f03..73dfdeb 100644
--- a/googletest/src/gtest-port.cc
+++ b/googletest/src/gtest-port.cc
@@ -715,7 +715,7 @@ RE::~RE() {
   free(const_cast<char*>(pattern_));
 }
 
-// Returns true if regular expression re matches the entire str.
+// Returns true if and only if regular expression re matches the entire str.
 bool RE::FullMatch(const char* str, const RE& re) {
   if (!re.is_valid_) return false;
 
@@ -723,8 +723,8 @@ bool RE::FullMatch(const char* str, const RE& re) {
   return regexec(&re.full_regex_, str, 1, &match, 0) == 0;
 }
 
-// Returns true if regular expression re matches a substring of str
-// (including str itself).
+// Returns true if and only if regular expression re matches a substring of
+// str (including str itself).
 bool RE::PartialMatch(const char* str, const RE& re) {
   if (!re.is_valid_) return false;
 
@@ -764,14 +764,14 @@ void RE::Init(const char* regex) {
 
 #elif GTEST_USES_SIMPLE_RE
 
-// Returns true if ch appears anywhere in str (excluding the
+// Returns true if and only if ch appears anywhere in str (excluding the
 // terminating '\0' character).
 bool IsInSet(char ch, const char* str) {
   return ch != '\0' && strchr(str, ch) != nullptr;
 }
 
-// Returns true if ch belongs to the given classification.  Unlike
-// similar functions in <ctype.h>, these aren't affected by the
+// Returns true if and only if ch belongs to the given classification.
+// Unlike similar functions in <ctype.h>, these aren't affected by the
 // current locale.
 bool IsAsciiDigit(char ch) { return '0' <= ch && ch <= '9'; }
 bool IsAsciiPunct(char ch) {
@@ -784,13 +784,13 @@ bool IsAsciiWordChar(char ch) {
       ('0' <= ch && ch <= '9') || ch == '_';
 }
 
-// Returns true if "\\c" is a supported escape sequence.
+// Returns true if and only if "\\c" is a supported escape sequence.
 bool IsValidEscape(char c) {
   return (IsAsciiPunct(c) || IsInSet(c, "dDfnrsStvwW"));
 }
 
-// Returns true if the given atom (specified by escaped and pattern)
-// matches ch.  The result is undefined if the atom is invalid.
+// Returns true if and only if the given atom (specified by escaped and
+// pattern) matches ch.  The result is undefined if the atom is invalid.
 bool AtomMatchesChar(bool escaped, char pattern_char, char ch) {
   if (escaped) {  // "\\p" where p is pattern_char.
     switch (pattern_char) {
@@ -828,7 +828,7 @@ bool ValidateRegex(const char* regex) {
 
   bool is_valid = true;
 
-  // True if ?, *, or + can follow the previous atom.
+  // True if and only if ?, *, or + can follow the previous atom.
   bool prev_repeatable = false;
   for (int i = 0; regex[i]; i++) {
     if (regex[i] == '\\') {  // An escape sequence
@@ -904,8 +904,8 @@ bool MatchRepetitionAndRegexAtHead(
   return false;
 }
 
-// Returns true if regex matches a prefix of str.  regex must be a
-// valid simple regular expression and not start with "^", or the
+// Returns true if and only if regex matches a prefix of str. regex must
+// be a valid simple regular expression and not start with "^", or the
 // result is undefined.
 bool MatchRegexAtHead(const char* regex, const char* str) {
   if (*regex == '\0')  // An empty regex matches a prefix of anything.
@@ -935,8 +935,8 @@ bool MatchRegexAtHead(const char* regex, const char* str) {
   }
 }
 
-// Returns true if regex matches any substring of str.  regex must be
-// a valid simple regular expression, or the result is undefined.
+// Returns true if and only if regex matches any substring of str.  regex must
+// be a valid simple regular expression, or the result is undefined.
 //
 // The algorithm is recursive, but the recursion depth doesn't exceed
 // the regex length, so we won't need to worry about running out of
@@ -964,13 +964,13 @@ RE::~RE() {
   free(const_cast<char*>(full_pattern_));
 }
 
-// Returns true if regular expression re matches the entire str.
+// Returns true if and only if regular expression re matches the entire str.
 bool RE::FullMatch(const char* str, const RE& re) {
   return re.is_valid_ && MatchRegexAnywhere(re.full_pattern_, str);
 }
 
-// Returns true if regular expression re matches a substring of str
-// (including str itself).
+// Returns true if and only if regular expression re matches a substring of
+// str (including str itself).
 bool RE::PartialMatch(const char* str, const RE& re) {
   return re.is_valid_ && MatchRegexAnywhere(re.pattern_, str);
 }
@@ -1330,7 +1330,7 @@ bool ParseInt32(const Message& src_text, const char* str, Int32* value) {
 // Reads and returns the Boolean environment variable corresponding to
 // the given flag; if it's not set, returns default_value.
 //
-// The value is considered true if it's not "0".
+// The value is considered true if and only if it's not "0".
 bool BoolFromGTestEnv(const char* flag, bool default_value) {
 #if defined(GTEST_GET_BOOL_FROM_ENV_)
   return GTEST_GET_BOOL_FROM_ENV_(flag, default_value);
diff --git a/googletest/src/gtest.cc b/googletest/src/gtest.cc
index cbd48d3..bd4ee42 100644
--- a/googletest/src/gtest.cc
+++ b/googletest/src/gtest.cc
@@ -177,8 +177,8 @@ namespace internal {
 // stack trace.
 const char kStackTraceMarker[] = "\nStack trace:\n";
 
-// g_help_flag is true if the --help flag or an equivalent form is
-// specified on the command line.
+// g_help_flag is true if and only if the --help flag or an equivalent form
+// is specified on the command line.
 bool g_help_flag = false;
 
 // Utilty function to Open File for Writing
@@ -217,12 +217,13 @@ GTEST_DEFINE_bool_(
 GTEST_DEFINE_bool_(
     break_on_failure,
     internal::BoolFromGTestEnv("break_on_failure", false),
-    "True if a failed assertion should be a debugger break-point.");
+    "True if and only if a failed assertion should be a debugger "
+    "break-point.");
 
 GTEST_DEFINE_bool_(
     catch_exceptions,
     internal::BoolFromGTestEnv("catch_exceptions", true),
-    "True if " GTEST_NAME_
+    "True if and only if " GTEST_NAME_
     " should catch exceptions and treat them as test failures.");
 
 GTEST_DEFINE_string_(
@@ -273,13 +274,13 @@ GTEST_DEFINE_string_(
 GTEST_DEFINE_bool_(
     print_time,
     internal::BoolFromGTestEnv("print_time", true),
-    "True if " GTEST_NAME_
+    "True if and only if " GTEST_NAME_
     " should display elapsed time in text output.");
 
 GTEST_DEFINE_bool_(
     print_utf8,
     internal::BoolFromGTestEnv("print_utf8", true),
-    "True if " GTEST_NAME_
+    "True if and only if " GTEST_NAME_
     " prints UTF8 characters as text.");
 
 GTEST_DEFINE_int32_(
@@ -296,13 +297,13 @@ GTEST_DEFINE_int32_(
 
 GTEST_DEFINE_bool_(
     show_internal_stack_frames, false,
-    "True if " GTEST_NAME_ " should include internal stack frames when "
+    "True if and only if " GTEST_NAME_ " should include internal stack frames when "
     "printing test failure stack traces.");
 
 GTEST_DEFINE_bool_(
     shuffle,
     internal::BoolFromGTestEnv("shuffle", false),
-    "True if " GTEST_NAME_
+    "True if and only if " GTEST_NAME_
     " should randomize tests' order on every run.");
 
 GTEST_DEFINE_int32_(
@@ -354,7 +355,7 @@ UInt32 Random::Generate(UInt32 range) {
   return state_ % range;
 }
 
-// GTestIsInitialized() returns true if the user has initialized
+// GTestIsInitialized() returns true if and only if the user has initialized
 // Google Test.  Useful for catching the user mistake of not initializing
 // Google Test before calling RUN_ALL_TESTS().
 static bool GTestIsInitialized() { return GetArgvs().size() > 0; }
@@ -371,18 +372,18 @@ static int SumOverTestSuiteList(const std::vector<TestSuite*>& case_list,
   return sum;
 }
 
-// Returns true if the test suite passed.
+// Returns true if and only if the test suite passed.
 static bool TestSuitePassed(const TestSuite* test_suite) {
   return test_suite->should_run() && test_suite->Passed();
 }
 
-// Returns true if the test suite failed.
+// Returns true if and only if the test suite failed.
 static bool TestSuiteFailed(const TestSuite* test_suite) {
   return test_suite->should_run() && test_suite->Failed();
 }
 
-// Returns true if test_suite contains at least one test that should
-// run.
+// Returns true if and only if test_suite contains at least one test that
+// should run.
 static bool ShouldRunTestSuite(const TestSuite* test_suite) {
   return test_suite->should_run();
 }
@@ -482,8 +483,8 @@ std::string UnitTestOptions::GetAbsolutePathToOutputFile() {
   return result.string();
 }
 
-// Returns true if the wildcard pattern matches the string.  The
-// first ':' or '\0' character in pattern marks the end of it.
+// Returns true if and only if the wildcard pattern matches the string.
+// The first ':' or '\0' character in pattern marks the end of it.
 //
 // This recursive algorithm isn't very efficient, but is clear and
 // works well enough for matching test names, which are short.
@@ -525,8 +526,8 @@ bool UnitTestOptions::MatchesFilter(
   }
 }
 
-// Returns true if the user-specified filter matches the test suite
-// name and the test name.
+// Returns true if and only if the user-specified filter matches the test
+// suite name and the test name.
 bool UnitTestOptions::FilterMatchesTest(const std::string& test_suite_name,
                                         const std::string& test_name) {
   const std::string& full_name = test_suite_name + "." + test_name.c_str();
@@ -910,7 +911,8 @@ const char* String::Utf16ToAnsi(LPCWSTR utf16_str)  {
 
 #endif  // GTEST_OS_WINDOWS_MOBILE
 
-// Compares two C strings.  Returns true if they have the same content.
+// Compares two C strings.  Returns true if and only if they have the same
+// content.
 //
 // Unlike strcmp(), this function can handle NULL argument(s).  A NULL
 // C string is considered different to any non-NULL C string,
@@ -1320,7 +1322,7 @@ std::vector<std::string> SplitEscapedString(const std::string& str) {
 //   lhs_value:      "5"
 //   rhs_value:      "6"
 //
-// The ignoring_case parameter is true if the assertion is a
+// The ignoring_case parameter is true if and only if the assertion is a
 // *_STRCASEEQ*.  When it's true, the string "Ignoring case" will
 // be inserted into the message.
 AssertionResult EqFailure(const char* lhs_expression,
@@ -1563,9 +1565,9 @@ namespace {
 
 // Helper functions for implementing IsSubString() and IsNotSubstring().
 
-// This group of overloaded functions return true if needle is a
-// substring of haystack.  NULL is considered a substring of itself
-// only.
+// This group of overloaded functions return true if and only if needle
+// is a substring of haystack.  NULL is considered a substring of
+// itself only.
 
 bool IsSubstringPred(const char* needle, const char* haystack) {
   if (needle == nullptr || haystack == nullptr) return needle == haystack;
@@ -1865,8 +1867,8 @@ std::string String::ShowWideCString(const wchar_t * wide_c_str) {
   return internal::WideStringToUtf8(wide_c_str, -1);
 }
 
-// Compares two wide C strings.  Returns true if they have the same
-// content.
+// Compares two wide C strings.  Returns true if and only if they have the
+// same content.
 //
 // Unlike wcscmp(), this function can handle NULL argument(s).  A NULL
 // C string is considered different to any non-NULL C string,
@@ -1910,7 +1912,7 @@ AssertionResult CmpHelperSTRNE(const char* s1_expression,
                             << " vs " << PrintToString(s2);
 }
 
-// Compares two C strings, ignoring case.  Returns true if they have
+// Compares two C strings, ignoring case.  Returns true if and only if they have
 // the same content.
 //
 // Unlike strcasecmp(), this function can handle NULL argument(s).  A
@@ -1922,18 +1924,18 @@ bool String::CaseInsensitiveCStringEquals(const char * lhs, const char * rhs) {
   return posix::StrCaseCmp(lhs, rhs) == 0;
 }
 
-  // Compares two wide C strings, ignoring case.  Returns true if they
-  // have the same content.
-  //
-  // Unlike wcscasecmp(), this function can handle NULL argument(s).
-  // A NULL C string is considered different to any non-NULL wide C string,
-  // including the empty string.
-  // NB: The implementations on different platforms slightly differ.
-  // On windows, this method uses _wcsicmp which compares according to LC_CTYPE
-  // environment variable. On GNU platform this method uses wcscasecmp
-  // which compares according to LC_CTYPE category of the current locale.
-  // On MacOS X, it uses towlower, which also uses LC_CTYPE category of the
-  // current locale.
+// Compares two wide C strings, ignoring case.  Returns true if and only if they
+// have the same content.
+//
+// Unlike wcscasecmp(), this function can handle NULL argument(s).
+// A NULL C string is considered different to any non-NULL wide C string,
+// including the empty string.
+// NB: The implementations on different platforms slightly differ.
+// On windows, this method uses _wcsicmp which compares according to LC_CTYPE
+// environment variable. On GNU platform this method uses wcscasecmp
+// which compares according to LC_CTYPE category of the current locale.
+// On MacOS X, it uses towlower, which also uses LC_CTYPE category of the
+// current locale.
 bool String::CaseInsensitiveWideCStringEquals(const wchar_t* lhs,
                                               const wchar_t* rhs) {
   if (lhs == nullptr) return rhs == nullptr;
@@ -1956,7 +1958,7 @@ bool String::CaseInsensitiveWideCStringEquals(const wchar_t* lhs,
 #endif  // OS selector
 }
 
-// Returns true if str ends with the given suffix, ignoring case.
+// Returns true if and only if str ends with the given suffix, ignoring case.
 // Any string is considered to end with an empty suffix.
 bool String::EndsWithCaseInsensitive(
     const std::string& str, const std::string& suffix) {
@@ -2198,12 +2200,12 @@ static bool TestPartSkipped(const TestPartResult& result) {
   return result.skipped();
 }
 
-// Returns true if the test was skipped.
+// Returns true if and only if the test was skipped.
 bool TestResult::Skipped() const {
   return !Failed() && CountIf(test_part_results_, TestPartSkipped) > 0;
 }
 
-// Returns true if the test failed.
+// Returns true if and only if the test failed.
 bool TestResult::Failed() const {
   for (int i = 0; i < total_part_count(); ++i) {
     if (GetTestPartResult(i).failed())
@@ -2212,22 +2214,22 @@ bool TestResult::Failed() const {
   return false;
 }
 
-// Returns true if the test part fatally failed.
+// Returns true if and only if the test part fatally failed.
 static bool TestPartFatallyFailed(const TestPartResult& result) {
   return result.fatally_failed();
 }
 
-// Returns true if the test fatally failed.
+// Returns true if and only if the test fatally failed.
 bool TestResult::HasFatalFailure() const {
   return CountIf(test_part_results_, TestPartFatallyFailed) > 0;
 }
 
-// Returns true if the test part non-fatally failed.
+// Returns true if and only if the test part non-fatally failed.
 static bool TestPartNonfatallyFailed(const TestPartResult& result) {
   return result.nonfatally_failed();
 }
 
-// Returns true if the test has a non-fatal failure.
+// Returns true if and only if the test has a non-fatal failure.
 bool TestResult::HasNonfatalFailure() const {
   return CountIf(test_part_results_, TestPartNonfatallyFailed) > 0;
 }
@@ -2523,18 +2525,18 @@ void Test::Run() {
       this, &Test::TearDown, "TearDown()");
 }
 
-// Returns true if the current test has a fatal failure.
+// Returns true if and only if the current test has a fatal failure.
 bool Test::HasFatalFailure() {
   return internal::GetUnitTestImpl()->current_test_result()->HasFatalFailure();
 }
 
-// Returns true if the current test has a non-fatal failure.
+// Returns true if and only if the current test has a non-fatal failure.
 bool Test::HasNonfatalFailure() {
   return internal::GetUnitTestImpl()->current_test_result()->
       HasNonfatalFailure();
 }
 
-// Returns true if the current test was skipped.
+// Returns true if and only if the current test was skipped.
 bool Test::IsSkipped() {
   return internal::GetUnitTestImpl()->current_test_result()->Skipped();
 }
@@ -2633,7 +2635,7 @@ class TestNameIs {
   explicit TestNameIs(const char* name)
       : name_(name) {}
 
-  // Returns true if the test name of test_info matches name_.
+  // Returns true if and only if the test name of test_info matches name_.
   bool operator()(const TestInfo * test_info) const {
     return test_info && test_info->name() == name_;
   }
@@ -2992,7 +2994,7 @@ static const char* GetAnsiColorCode(GTestColor color) {
 
 #endif  // GTEST_OS_WINDOWS && !GTEST_OS_WINDOWS_MOBILE
 
-// Returns true if Google Test should use colors in the output.
+// Returns true if and only if Google Test should use colors in the output.
 bool ShouldUseColor(bool stdout_is_tty) {
   const char* const gtest_color = GTEST_FLAG(color).c_str();
 
@@ -4709,11 +4711,12 @@ internal::TimeInMillis UnitTest::elapsed_time() const {
   return impl()->elapsed_time();
 }
 
-// Returns true if the unit test passed (i.e. all test suites passed).
+// Returns true if and only if the unit test passed (i.e. all test suites
+// passed).
 bool UnitTest::Passed() const { return impl()->Passed(); }
 
-// Returns true if the unit test failed (i.e. some test suite failed
-// or something outside of all tests failed).
+// Returns true if and only if the unit test failed (i.e. some test suite
+// failed or something outside of all tests failed).
 bool UnitTest::Failed() const { return impl()->Failed(); }
 
 // Gets the i-th test suite among all the test suites. i can range from 0 to
@@ -5161,7 +5164,7 @@ class TestSuiteNameIs {
   // Constructor.
   explicit TestSuiteNameIs(const std::string& name) : name_(name) {}
 
-  // Returns true if the name of test_suite matches name_.
+  // Returns true if and only if the name of test_suite matches name_.
   bool operator()(const TestSuite* test_suite) const {
     return test_suite != nullptr &&
            strcmp(test_suite->name(), name_.c_str()) == 0;
@@ -5232,7 +5235,8 @@ static void TearDownEnvironment(Environment* env) { env->TearDown(); }
 // All other functions called from RunAllTests() may safely assume that
 // parameterized tests are ready to be counted and run.
 bool UnitTestImpl::RunAllTests() {
-  // True if Google Test is initialized before RUN_ALL_TESTS() is called.
+  // True if and only if Google Test is initialized before RUN_ALL_TESTS() is
+  // called.
   const bool gtest_is_initialized_before_run_all_tests = GTestIsInitialized();
 
   // Do not run any test if the --help flag was specified.
@@ -5248,7 +5252,7 @@ bool UnitTestImpl::RunAllTests() {
   // protocol.
   internal::WriteToShardStatusFileIfNeeded();
 
-  // True if we are in a subprocess for running a thread-safe-style
+  // True if and only if we are in a subprocess for running a thread-safe-style
   // death test.
   bool in_subprocess_for_death_test = false;
 
@@ -5281,7 +5285,7 @@ bool UnitTestImpl::RunAllTests() {
   random_seed_ = GTEST_FLAG(shuffle) ?
       GetRandomSeedFromFlag(GTEST_FLAG(random_seed)) : 0;
 
-  // True if at least one test has failed.
+  // True if and only if at least one test has failed.
   bool failed = false;
 
   TestEventListener* repeater = listeners()->repeater();
@@ -5479,8 +5483,8 @@ Int32 Int32FromEnvOrDie(const char* var, Int32 default_val) {
 }
 
 // Given the total number of shards, the shard index, and the test id,
-// returns true if the test should be run on this shard. The test id is
-// some arbitrary but unique non-negative integer assigned to each test
+// returns true if and only if the test should be run on this shard. The test id
+// is some arbitrary but unique non-negative integer assigned to each test
 // method. Assumes that 0 <= shard_index < total_shards.
 bool ShouldRunTestOnShard(int total_shards, int shard_index, int test_id) {
   return (test_id % total_shards) == shard_index;
@@ -6053,7 +6057,7 @@ void ParseGoogleTestFlagsOnlyImpl(int* argc, CharType** argv) {
 void ParseGoogleTestFlagsOnly(int* argc, char** argv) {
   ParseGoogleTestFlagsOnlyImpl(argc, argv);
 
-  // Fix the value of *_NSGetArgc() on macOS, but if
+  // Fix the value of *_NSGetArgc() on macOS, but if and only if
   // *_NSGetArgv() == argv
   // Only applicable to char** version of argv
 #if GTEST_OS_MAC
diff --git a/googletest/test/googletest-death-test-test.cc b/googletest/test/googletest-death-test-test.cc
index 814d771..cba906c 100644
--- a/googletest/test/googletest-death-test-test.cc
+++ b/googletest/test/googletest-death-test-test.cc
@@ -141,7 +141,7 @@ class TestForDeathTest : public testing::Test {
       DieInside("MemberFunction");
   }
 
-  // True if MemberFunction() should die.
+  // True if and only if MemberFunction() should die.
   bool should_die_;
   const FilePath original_dir_;
 };
@@ -158,7 +158,7 @@ class MayDie {
   }
 
  private:
-  // True if MemberFunction() should die.
+  // True if and only if MemberFunction() should die.
   bool should_die_;
 };
 
@@ -573,8 +573,8 @@ TEST_F(TestForDeathTest, ErrorMessageMismatch) {
   }, "died but not with expected error");
 }
 
-// On exit, *aborted will be true if the EXPECT_DEATH() statement
-// aborted the function.
+// On exit, *aborted will be true if and only if the EXPECT_DEATH()
+// statement aborted the function.
 void ExpectDeathTestHelper(bool* aborted) {
   *aborted = true;
   EXPECT_DEATH(DieIf(false), "DieIf");  // This assertion should fail.
diff --git a/googletest/test/googletest-throw-on-failure-test.py b/googletest/test/googletest-throw-on-failure-test.py
index a38cd33..ea627c4 100755
--- a/googletest/test/googletest-throw-on-failure-test.py
+++ b/googletest/test/googletest-throw-on-failure-test.py
@@ -86,7 +86,7 @@ class ThrowOnFailureTest(gtest_test_utils.TestCase):
                         variable; None if the variable should be unset.
       flag_value:       value of the --gtest_break_on_failure flag;
                         None if the flag should not be present.
-      should_fail:      True if the program is expected to fail.
+      should_fail:      True if and only if the program is expected to fail.
     """
 
     SetEnvVar(THROW_ON_FAILURE, env_var_value)
diff --git a/googletest/test/gtest_environment_test.cc b/googletest/test/gtest_environment_test.cc
index 58908e6..064bfc5 100644
--- a/googletest/test/gtest_environment_test.cc
+++ b/googletest/test/gtest_environment_test.cc
@@ -116,7 +116,7 @@ void Check(bool condition, const char* msg) {
   }
 }
 
-// Runs the tests.  Return true if successful.
+// Runs the tests.  Return true if and only if successful.
 //
 // The 'failure' parameter specifies the type of failure that should
 // be generated by the global set-up.
diff --git a/googletest/test/gtest_pred_impl_unittest.cc b/googletest/test/gtest_pred_impl_unittest.cc
index 4d77896..1afe5e2 100644
--- a/googletest/test/gtest_pred_impl_unittest.cc
+++ b/googletest/test/gtest_pred_impl_unittest.cc
@@ -144,10 +144,10 @@ class Predicate1Test : public testing::Test {
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -539,10 +539,10 @@ class Predicate2Test : public testing::Test {
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -976,10 +976,10 @@ class Predicate3Test : public testing::Test {
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -1455,10 +1455,10 @@ class Predicate4Test : public testing::Test {
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -1976,10 +1976,10 @@ class Predicate5Test : public testing::Test {
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
diff --git a/googletest/test/gtest_premature_exit_test.cc b/googletest/test/gtest_premature_exit_test.cc
index 777a8bf..1d1187e 100644
--- a/googletest/test/gtest_premature_exit_test.cc
+++ b/googletest/test/gtest_premature_exit_test.cc
@@ -45,7 +45,7 @@ namespace {
 
 class PrematureExitTest : public Test {
  public:
-  // Returns true if the given file exists.
+  // Returns true if and only if the given file exists.
   static bool FileExists(const char* filepath) {
     StatStruct stat;
     return Stat(filepath, &stat) == 0;
@@ -61,7 +61,7 @@ class PrematureExitTest : public Test {
     }
   }
 
-  // Returns true if the premature-exit file exists.
+  // Returns true if and only if the premature-exit file exists.
   bool PrematureExitFileExists() const {
     return FileExists(premature_exit_file_path_);
   }
diff --git a/googletest/test/gtest_test_utils.py b/googletest/test/gtest_test_utils.py
index abd56ec..3db665e 100755
--- a/googletest/test/gtest_test_utils.py
+++ b/googletest/test/gtest_test_utils.py
@@ -215,10 +215,10 @@ class Subprocess:
     Returns:
       An object that represents outcome of the executed process. It has the
       following attributes:
-        terminated_by_signal   True if the child process has been terminated
-                               by a signal.
+        terminated_by_signal   True if and only if the child process has been
+                               terminated by a signal.
         signal                 Sygnal that terminated the child process.
-        exited                 True if the child process exited normally.
+        exited                 True if and only if the child process exited normally.
         exit_code              The code with which the child process exited.
         output                 Child process's stdout and stderr output
                                combined in a string.
diff --git a/googletest/test/gtest_unittest.cc b/googletest/test/gtest_unittest.cc
index 2b00b70..220ceba 100644
--- a/googletest/test/gtest_unittest.cc
+++ b/googletest/test/gtest_unittest.cc
@@ -2170,12 +2170,12 @@ static Environment* record_property_env GTEST_ATTRIBUTE_UNUSED_ =
 
 // First, some predicates and predicate-formatters needed by the tests.
 
-// Returns true if the argument is an even number.
+// Returns true if and only if the argument is an even number.
 bool IsEven(int n) {
   return (n % 2) == 0;
 }
 
-// A functor that returns true if the argument is an even number.
+// A functor that returns true if and only if the argument is an even number.
 struct IsEvenFunctor {
   bool operator()(int n) { return IsEven(n); }
 };
@@ -2219,13 +2219,13 @@ struct AssertIsEvenFunctor {
   }
 };
 
-// Returns true if the sum of the arguments is an even number.
+// Returns true if and only if the sum of the arguments is an even number.
 bool SumIsEven2(int n1, int n2) {
   return IsEven(n1 + n2);
 }
 
-// A functor that returns true if the sum of the arguments is an even
-// number.
+// A functor that returns true if and only if the sum of the arguments is an
+// even number.
 struct SumIsEven3Functor {
   bool operator()(int n1, int n2, int n3) {
     return IsEven(n1 + n2 + n3);