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+#include "erfa.h"
+
+double eraObl80(double date1, double date2)
+/*
+** - - - - - - - - -
+** e r a O b l 8 0
+** - - - - - - - - -
+**
+** Mean obliquity of the ecliptic, IAU 1980 model.
+**
+** Given:
+** date1,date2 double TT as a 2-part Julian Date (Note 1)
+**
+** Returned (function value):
+** double obliquity of the ecliptic (radians, Note 2)
+**
+** Notes:
+**
+** 1) The TT date date1+date2 is a Julian Date, apportioned in any
+** convenient way between the two arguments. For example,
+** JD(TT)=2450123.7 could be expressed in any of these ways,
+** among others:
+**
+** date1 date2
+**
+** 2450123.7 0.0 (JD method)
+** 2451545.0 -1421.3 (J2000 method)
+** 2400000.5 50123.2 (MJD method)
+** 2450123.5 0.2 (date & time method)
+**
+** The JD method is the most natural and convenient to use in
+** cases where the loss of several decimal digits of resolution
+** is acceptable. The J2000 method is best matched to the way
+** the argument is handled internally and will deliver the
+** optimum resolution. The MJD method and the date & time methods
+** are both good compromises between resolution and convenience.
+**
+** 2) The result is the angle between the ecliptic and mean equator of
+** date date1+date2.
+**
+** Reference:
+**
+** Explanatory Supplement to the Astronomical Almanac,
+** P. Kenneth Seidelmann (ed), University Science Books (1992),
+** Expression 3.222-1 (p114).
+**
+** Copyright (C) 2013-2014, NumFOCUS Foundation.
+** Derived, with permission, from the SOFA library. See notes at end of file.
+*/
+{
+ double t, eps0;
+
+
+/* Interval between fundamental epoch J2000.0 and given date (JC). */
+ t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
+
+/* Mean obliquity of date. */
+ eps0 = ERFA_DAS2R * (84381.448 +
+ (-46.8150 +
+ (-0.00059 +
+ ( 0.001813) * t) * t) * t);
+
+ return eps0;
+
+}
+/*----------------------------------------------------------------------
+**
+**
+** Copyright (C) 2013-2014, NumFOCUS Foundation.
+** All rights reserved.
+**
+** This library is derived, with permission, from the International
+** Astronomical Union's "Standards of Fundamental Astronomy" library,
+** available from http://www.iausofa.org.
+**
+** The ERFA version is intended to retain identical functionality to
+** the SOFA library, but made distinct through different function and
+** file names, as set out in the SOFA license conditions. The SOFA
+** original has a role as a reference standard for the IAU and IERS,
+** and consequently redistribution is permitted only in its unaltered
+** state. The ERFA version is not subject to this restriction and
+** therefore can be included in distributions which do not support the
+** concept of "read only" software.
+**
+** Although the intent is to replicate the SOFA API (other than
+** replacement of prefix names) and results (with the exception of
+** bugs; any that are discovered will be fixed), SOFA is not
+** responsible for any errors found in this version of the library.
+**
+** If you wish to acknowledge the SOFA heritage, please acknowledge
+** that you are using a library derived from SOFA, rather than SOFA
+** itself.
+**
+**
+** TERMS AND CONDITIONS
+**
+** Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions
+** are met:
+**
+** 1 Redistributions of source code must retain the above copyright
+** notice, this list of conditions and the following disclaimer.
+**
+** 2 Redistributions in binary form must reproduce the above copyright
+** notice, this list of conditions and the following disclaimer in
+** the documentation and/or other materials provided with the
+** distribution.
+**
+** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
+** the International Astronomical Union nor the names of its
+** contributors may be used to endorse or promote products derived
+** from this software without specific prior written permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+** POSSIBILITY OF SUCH DAMAGE.
+**
+*/