Do not require the SmallGrp package

CHANGES.md

@@ -5,6 +5,11 @@
   - An operation `ClassTranspositionConjugationBall` has been added,
     together with a method for rcwa groups over Z.
     (Not documented so far.)
+  - RCWA no longer requires the SmallGrp package: viewing and displaying
+    an rcwa group used the attribute `IdGroup` and its tester
+    `HasIdGroup`, which are provided by that package, and thus failed if
+    it was not loaded. The isomorphism type is still shown whenever
+    `IdGroup` is known, and the order is printed otherwise.
 
 ## Changes between RCWA 4.8.0 and RCWA 4.9.0 (May 4, 2026):
 

lib/rcwagrp.gi

@@ -14,6 +14,21 @@
 ##
 #############################################################################
 
+#############################################################################
+##
+#F  RCWA_HasIdGroup( <G> ) . . . . . . . . . . `HasIdGroup', if it is present
+#F  RCWA_IdGroup( <G> ) . . . . . . . . . . . . . `IdGroup', if it is present
+##
+##  The attribute `IdGroup' and its tester `HasIdGroup' are provided by the
+##  SmallGrp package, which is not always available. Since only SmallGrp can
+##  set that attribute, it is certainly not set if the package is missing,
+##  so treating it as unset in that case is safe. These two functions are
+##  used purely to enrich `ViewObj' and `Display' output.
+##
+BindGlobal( "RCWA_HasIdGroup",
+            G -> IsBound( HasIdGroup ) and ValueGlobal( "HasIdGroup" )( G ) );
+BindGlobal( "RCWA_IdGroup", G -> ValueGlobal( "IdGroup" )( G ) );
+
 #############################################################################
 ##
 #S  Implications between the categories of rcwa groups. /////////////////////
@@ -222,8 +237,8 @@ InstallMethod( ViewObj,
       Print("rcwa group over ",RingString," with ",NrGens," generator");
       if NrGens > 1 then Print("s"); fi;
       if not (HasIsTame(G) and not IsTame(G)) then
-        if   HasIdGroup(G)
-        then Print(", of isomorphism type ",IdGroup(G));
+        if   RCWA_HasIdGroup(G)
+        then Print(", of isomorphism type ",RCWA_IdGroup(G));
         elif HasSize(G)
         then Print(", of order ",Size(G)); fi;
       fi;
@@ -329,8 +344,9 @@ InstallMethod( Display,
          if prefix then Print("rcwa "); else Print("\nRcwa "); fi;
          Print("group over ",RingString);
          if not (HasIsTame(G) and not IsTame(G)) then
-           if   HasIdGroup(G) then Print(" of isomorphism type ",IdGroup(G));
-           elif HasSize(G)    then Print(" of order ",Size(G)); fi;
+           if   RCWA_HasIdGroup(G)
+           then Print(" of isomorphism type ",RCWA_IdGroup(G));
+           elif HasSize(G) then Print(" of order ",Size(G)); fi;
          fi;
          Print(", generated by\n\n[\n");
          for g in GeneratorsOfGroup(G) do Display(g); od;

tst/integral.tst

@@ -1111,10 +1111,15 @@ gap> IsBijective(phi);
 true
 gap> Size(Image(phi));
 24
+#@if IsPackageMarkedForLoading( "smallgrp", "" )
 gap> IdGroup(G);
 [ 24, 12 ]
 gap> G;
 <rcwa group over Z with 2 generators, of isomorphism type [ 24, 12 ]>
+#@else
+gap> G;
+<rcwa group over Z with 2 generators, of order 24>
+#@fi
 gap> Modulus(G);
 6
 gap> A4 := DerivedSubgroup(G);
@@ -2023,12 +2028,16 @@ gap> StructureDescription(G);
 "C2 x C2"
 gap> G := Group(ClassTransposition(0,4,1,4),ClassShift(0,4),
 >               ClassReflection(1,4),ClassReflection(2,4),ClassShift(3,4));;
+#@if IsPackageMarkedForLoading( "smallgrp", "" )
 gap> StructureDescription(G:short);
 "Z^2.((S3xS3):2)x2xZ"
+#@fi
 gap> G := Group(ClassTransposition(0,2,1,4),
 >               ClassShift(2,4),ClassReflection(1,2));;
+#@if IsPackageMarkedForLoading( "smallgrp", "" )
 gap> StructureDescription(G:short);
 "Z^2.((S3xS3):2)"
+#@fi
 gap> G := Group(ClassTransposition(0,2,1,4),ClassShift(0,5));;
 gap> StructureDescription(G);
 "(Z x Z x Z x Z x Z x Z x Z) . (C2 x S7)"