Fix ShallowCopy for KnuthBendixRewritingSystem

ShallowCopy did not copy the components `freefam`, `ordering` and `tzordering`
of a KnuthBendixRewritingSystem, and hence cause an error if a rewriting system
was ShallowCopied and used afterwards.

lib/kbsemi.gi

@@ -787,7 +787,9 @@ InstallMethod( ShallowCopy,
                   reduced := false,
                   tzrules:= StructuralCopy(kbrws!.tzrules),
                   pairs2check:= [],
-                  ordering :=kbrws!.ordering)));
+                  ordering :=kbrws!.ordering,
+                  freefam := kbrws!.freefam,
+                  tzordering := kbrws!.tzordering)));
 
 ###############################################################################
 ##

tst/testinstall/kbsemi.tst

@@ -0,0 +1,95 @@
+gap> START_TEST("kbsemi.tst");
+gap> F:=FreeGroup(2);
+<free group on the generators [ f1, f2 ]>
+gap> mhom:=IsomorphismFpMonoid(F);;
+gap> mon:=Image(mhom);
+<fp monoid on the generators [ f1, f1^-1, f2, f2^-1 ]>
+gap> k:=KnuthBendixRewritingSystem(mon);
+Knuth Bendix Rewriting System for Monoid( [ f1, f1^-1, f2, f2^-1 
+ ] ) with rules 
+[ [ f1*f1^-1, <identity ...> ], [ f1^-1*f1, <identity ...> ], 
+  [ f2*f2^-1, <identity ...> ], [ f2^-1*f2, <identity ...> ] ]
+gap> k1:=ShallowCopy(k);
+Knuth Bendix Rewriting System for Monoid( [ f1, f1^-1, f2, f2^-1 
+ ] ) with rules 
+[ [ f1*f1^-1, <identity ...> ], [ f1^-1*f1, <identity ...> ], 
+  [ f2*f2^-1, <identity ...> ], [ f2^-1*f2, <identity ...> ] ]
+gap> MakeKnuthBendixRewritingSystemConfluent(k1);
+gap> k = k1;
+true
+
+#
+gap> f := FreeSemigroup("a","b");;
+gap> a := f.1;; b := f.2;;
+gap> s := f/[[a*b,b],[b*a,a]];;
+gap> rws := KnuthBendixRewritingSystem(s);
+Knuth Bendix Rewriting System for Semigroup( [ a, b ] ) with rules 
+[ [ a*b, b ], [ b*a, a ] ]
+gap> IsConfluent(rws);
+false
+gap> rws1 := ShallowCopy(rws);
+Knuth Bendix Rewriting System for Semigroup( [ a, b ] ) with rules 
+[ [ a*b, b ], [ b*a, a ] ]
+gap> rws1 = rws;
+true
+gap> IsConfluent(rws1);
+false
+gap> MakeKnuthBendixRewritingSystemConfluent(rws1);
+gap> rws1 = rws;
+false
+gap> MakeKnuthBendixRewritingSystemConfluent(rws);
+gap> rws1 = rws;
+true
+
+# Some more tests for Knuth-Bendix rewriting
+gap> CreateKnuthBendixRewritingSystem(FamilyObj(1), x -> x);
+Error, Can only create a KB rewriting system for an fp semigroup or monoid
+gap> M := FreeMonoid(2);; N := M / [ [M.1, M.2] ];;
+gap> CreateKnuthBendixRewritingSystem(FamilyObj(Representative(N)), x -> x);
+Error, Second argument must be a reduction ordering
+gap> kbrws := KnuthBendixRewritingSystem(N);
+Knuth Bendix Rewriting System for Monoid( [ m1, m2 ] ) with rules 
+[ [ m2, m1 ] ]
+gap> kbrws := KnuthBendixRewritingSystem(N, {x,y} -> [y,x]);
+Error, <expr> must be 'true' or 'false' (not a list (plain,dense))
+gap> kbrws := KnuthBendixRewritingSystem(N, \<);
+Knuth Bendix Rewriting System for Monoid( [ m1, m2 ] ) with rules 
+[ [ m2, m1 ] ]
+gap> F := FreeGroup(2);; G := F / [ F.1^2, F.2^2, (F.1 * F.2)^6 ];;
+gap> kbrws := KnuthBendixRewritingSystem(Image(IsomorphismFpMonoid(G)));;
+gap> IsConfluent(kbrws);
+false
+gap> IsReduced(kbrws);
+true
+gap> kbrws2 := ShallowCopy(kbrws);
+Knuth Bendix Rewriting System for Monoid( [ f1, f1^-1, f2, f2^-1 
+ ] ) with rules 
+[ [ f1^2, <identity ...> ], [ f1*f1^-1, <identity ...> ], 
+  [ f1^-1*f1, <identity ...> ], [ f2^2, <identity ...> ], 
+  [ f2*f2^-1, <identity ...> ], [ f2^-1*f2, <identity ...> ], 
+  [ (f1*f2)^6, <identity ...> ] ]
+gap> kbrws = kbrws2;
+true
+gap> IsConfluent(kbrws2);
+false
+gap> IsReduced(kbrws2);
+true
+gap> MakeKnuthBendixRewritingSystemConfluent(kbrws);
+gap> IsConfluent(kbrws);
+true
+gap> IsConfluent(kbrws2);
+false
+gap> kbrws = kbrws2;
+false
+gap> S := FreeSemigroup(2);; T := S / [ [S.1, S.2] ];;
+gap> KnuthBendixRewritingSystem(S, \<);
+Error, no method found! For debugging hints type ?Recovery from NoMethodFound
+Error, no 1st choice method found for `KnuthBendixRewritingSystem' on 2 argume\
+nts
+gap> M := FreeMonoid(2);; N := M / [ [M.1, M.2] ];;
+gap> KnuthBendixRewritingSystem(N, \<);
+Knuth Bendix Rewriting System for Monoid( [ m1, m2 ] ) with rules 
+[ [ m2, m1 ] ]
+
+#
+gap> STOP_TEST("kbsemi.tst");