Fix bug in OneCoboundariesCR

It which lead to an error in OneCohomologyCR.

Fixes #25

CHANGES.md

@@ -1,5 +1,10 @@
 This file describes changes in the GAP package 'polycyclic'.
 
+X.YY (YYYY-MM-D)
+
+  * Fixed a bug in OneCoboundariesCR which lead to an error in OneCohomologyCR
+  * ...
+
 2.13.1 (2018-04-27)
 
   * Removed a regression test case which failed if no other packages are loaded

gap/cohom/onecohom.gi

@@ -56,7 +56,7 @@ InstallGlobalFunction( OneCoboundariesEX, function( A )
 end );
 
 InstallGlobalFunction( OneCoboundariesCR, function( A )
-    return OneCoboundariesEX( A );
+    return OneCoboundariesEX( A ).basis;
 end );
 
 #############################################################################

tst/bugfix.tst

@@ -355,5 +355,22 @@ gap> N := NormalizerPcpGroup( G, U );;
 gap> Images(iso, Normalizer( P2, PreImages(iso, U) )) = N;
 true
 
+#
+# Fix a bug in OneCoboundariesCR which lead to an error in OneCohomologyCR.
+# <https://github.com/gap-packages/polycyclic/issues/25>
+#
+gap> G:=HeisenbergPcpGroup(1);
+Pcp-group with orders [ 0, 0, 0 ]
+gap> N:=Center(G);
+Pcp-group with orders [ 0 ]
+gap> C:=CRRecordBySubgroup(G,N);;
+gap> OneCoboundariesCR(C);
+[  ]
+gap> OneCohomologyCR(C);
+rec( 
+  factor := rec( denom := [  ], gens := [ [ 1, 0 ], [ 0, 1 ] ], 
+      imgs := [ [ 1, 0 ], [ 0, 1 ] ], prei := [ [ 1, 0 ], [ 0, 1 ] ], 
+      rels := [ 0, 0 ] ), gcb := [  ], gcc := [ [ 1, 0 ], [ 0, 1 ] ] )
+
 #
 gap> STOP_TEST( "bugfix.tst", 10000000);