From 1e942d91f2bf77fcfb1683e72feb591c17d1a5b3 Mon Sep 17 00:00:00 2001
From: stertooy <5571903+stertooy@users.noreply.github.com>
Date: Thu, 15 Oct 2026 12:58:13 +0200
Subject: [PATCH] Fix CRRecordBYPcp for non-snf pcps

---
 CHANGES.md              |  1 +
 gap/cohom/cohom.gi      |  7 +++++++
 tst/bugfix/gh-00260.tst | 17 +++++++++++++++++
 3 files changed, 25 insertions(+)
 create mode 100644 tst/bugfix/gh-00260.tst

diff --git a/CHANGES.md b/CHANGES.md
index 83be3501..a74f14ec 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -14,6 +14,7 @@ This file describes changes in the GAP package 'polycyclic'.
   - `ComplementClassesCR`
   - `ConjugacyElementsBySeries`
   - `ConjugacyIntegralAction`
+  - `CRRecordByPcp`
   - `FCCentre`
   - `IsElementaryAbelian`
   - `IsMatrixRepresentation`
diff --git a/gap/cohom/cohom.gi b/gap/cohom/cohom.gi
index fd2e7ddb..d3014ca5 100644
--- a/gap/cohom/cohom.gi
+++ b/gap/cohom/cohom.gi
@@ -307,6 +307,13 @@ end );
 BindGlobal( "CRRecordByPcp", function( G, pcp )
     local A;
 
+    # compute snf if needed
+    if not IsSNFPcp( pcp ) and
+       Length( Set( RelativeOrdersOfPcp( pcp ) ) ) > 1 then
+        pcp := Pcp( GroupOfPcp( pcp ),
+                    SubgroupByIgs( G, DenominatorOfPcp( pcp ) ), "snf" );
+    fi;
+
     # set up record
     A := rec( group  := G,
               factor := Pcp( G, GroupOfPcp( pcp ) ),
diff --git a/tst/bugfix/gh-00260.tst b/tst/bugfix/gh-00260.tst
new file mode 100644
index 00000000..faf562d0
--- /dev/null
+++ b/tst/bugfix/gh-00260.tst
@@ -0,0 +1,17 @@
+gap> START_TEST( "gh-00260.tst" );
+
+#
+# Fix CRRecordByPcp for non-snf pcp's
+# <https://github.com/gap-packages/polycyclic/issues/260>
+#
+gap> G := AbelianPcpGroup( 2 );;
+gap> Q := G / Subgroup( G, [ G.1^6 * G.2 ] );;
+gap> IsFreeAbelian( Q );
+true
+gap> CRRecordByPcp( Q, Pcp( Q, "snf" ) ).dim;
+1
+gap> CRRecordByPcp( Q, Pcp( Q ) ).dim;
+1
+
+#
+gap> STOP_TEST( "gh-00260.tst" );