Congruence classes are associative (resolves #800)

Author: james-d-mitchell

gap/semigroups/semiquo.gd

@@ -10,3 +10,5 @@
 
 DeclareAttribute("OneImmutable", IsQuotientSemigroup);
 DeclareOperation("\/", [IsSemigroup, IsSemigroupIdeal]);
+
+InstallTrueMethod(IsAssociativeElement, IsCongruenceClass);

tst/testinstall.tst

@@ -1760,6 +1760,12 @@ gap> Matrix(GF(4), One(S));;
 gap> Size(Elements(S));
 16
 
+# Issue 800, Quotient semigroup elements are not associative
+gap> T := FullTransformationMonoid(2);;
+gap> cong := SemigroupCongruence(T, []);;
+gap> IsAssociativeElement(Elements(T / cong)[1]);
+true
+
 # SEMIGROUPS_UnbindVariables
 gap> Unbind(B);
 gap> Unbind(D);