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diff --git a/math/slalib/xy2xy.f b/math/slalib/xy2xy.f
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+      SUBROUTINE slXYXY (X1,Y1,COEFFS,X2,Y2)
+*+
+*     - - - - - -
+*      X Y X Y
+*     - - - - - -
+*
+*  Transform one [X,Y] into another using a linear model of the type
+*  produced by the slFTXY routine.
+*
+*  Given:
+*     X1       d        x-coordinate
+*     Y1       d        y-coordinate
+*     COEFFS  d(6)      transformation coefficients (see note)
+*
+*  Returned:
+*     X2       d        x-coordinate
+*     Y2       d        y-coordinate
+*
+*  The model relates two sets of [X,Y] coordinates as follows.
+*  Naming the elements of COEFFS:
+*
+*     COEFFS(1) = A
+*     COEFFS(2) = B
+*     COEFFS(3) = C
+*     COEFFS(4) = D
+*     COEFFS(5) = E
+*     COEFFS(6) = F
+*
+*  the present routine performs the transformation:
+*
+*     X2 = A + B*X1 + C*Y1
+*     Y2 = D + E*X1 + F*Y1
+*
+*  See also slFTXY, slPXY, slINVF, slDCMF
+*
+*  P.T.Wallace   Starlink   5 December 1994
+*
+*  Copyright (C) 1995 Rutherford Appleton Laboratory
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the
+*    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+*    Boston, MA  02110-1301  USA
+*
+*  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION X1,Y1,COEFFS(6),X2,Y2
+
+
+      X2=COEFFS(1)+COEFFS(2)*X1+COEFFS(3)*Y1
+      Y2=COEFFS(4)+COEFFS(5)*X1+COEFFS(6)*Y1
+
+      END