Add another ViewString method for inverse semigroups

This commit introduces a method for ViewString for semigroups satisfying
IsInverseSemigroup and HasGeneratorsOfSemigroup.  The rank of the filter
IsSemigroup and HasGeneratorsOfSemigroup is 14, whereas the rank of
IsInverseSemigroup is 21. Previously, if a semigroup learned that it was
inverse but did not have GeneratorsOfInverseSemigroup, then the default
ViewString method for IsInverseSemigroup was used. With this commit the
more elaborate _ViewStringForSemigroups is used instead.

lib/semigrp.gi

@@ -113,6 +113,10 @@ InstallMethod(ViewString, "for a semigroup with generators",
 InstallMethod(ViewString, "for a monoid with generators",
 [IsMonoid and HasGeneratorsOfMonoid], _ViewStringForSemigroups);
 
+InstallMethod(ViewString, "for an inverse semigroup with generators",
+[IsInverseSemigroup and HasGeneratorsOfSemigroup],
+_ViewStringForSemigroups);
+
 InstallMethod(ViewString, "for an inverse semigroup with generators",
 [IsInverseSemigroup and HasGeneratorsOfInverseSemigroup],
 _ViewStringForSemigroups);

tst/testinstall/semigrp.tst

@@ -431,6 +431,19 @@ false
 gap> IsEmpty(T);
 true
 
+# Check for correct ViewString method for IsInverseSemigroup and
+# HasGeneratorsOfSemigroup
+gap> S := Semigroup(Transformation([4, 3, 5, 5, 5]),
+>                   Transformation([4, 1, 5, 2, 5]), 
+>                   Transformation([5, 5, 2, 1, 5]));
+<transformation semigroup of degree 5 with 3 generators>
+gap> IsInverseSemigroup(S);
+true
+gap> Size(S);
+36
+gap> S;
+<inverse transformation semigroup of size 36, degree 5 with 3 generators>
+
 #
 gap> STOP_TEST( "semigrp.tst", 1060000);