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diff --git a/ast/erfa/sepp.c b/ast/erfa/sepp.c
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+++ b/ast/erfa/sepp.c
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+#include "erfa.h"
+
+double eraSepp(double a[3], double b[3])
+/*
+**  - - - - - - - -
+**   e r a S e p p
+**  - - - - - - - -
+**
+**  Angular separation between two p-vectors.
+**
+**  Given:
+**     a      double[3]    first p-vector (not necessarily unit length)
+**     b      double[3]    second p-vector (not necessarily unit length)
+**
+**  Returned (function value):
+**            double       angular separation (radians, always positive)
+**
+**  Notes:
+**
+**  1) If either vector is null, a zero result is returned.
+**
+**  2) The angular separation is most simply formulated in terms of
+**     scalar product.  However, this gives poor accuracy for angles
+**     near zero and pi.  The present algorithm uses both cross product
+**     and dot product, to deliver full accuracy whatever the size of
+**     the angle.
+**
+**  Called:
+**     eraPxp       vector product of two p-vectors
+**     eraPm        modulus of p-vector
+**     eraPdp       scalar product of two p-vectors
+**
+**  Copyright (C) 2013-2016, NumFOCUS Foundation.
+**  Derived, with permission, from the SOFA library.  See notes at end of file.
+*/
+{
+   double axb[3], ss, cs, s;
+
+
+/* Sine of angle between the vectors, multiplied by the two moduli. */
+   eraPxp(a, b, axb);
+   ss = eraPm(axb);
+
+/* Cosine of the angle, multiplied by the two moduli. */
+   cs = eraPdp(a, b);
+
+/* The angle. */
+   s = ((ss != 0.0) || (cs != 0.0)) ? atan2(ss, cs) : 0.0;
+
+   return s;
+
+}
+/*----------------------------------------------------------------------
+**  
+**  
+**  Copyright (C) 2013-2016, 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.
+**  
+*/