From f56c5e3451d4fe90f96c7100bdb5f9b909c65f28 Mon Sep 17 00:00:00 2001
From: James Mitchell <jdm3@st-andrews.ac.uk>
Date: Tue, 5 Jan 2016 20:39:02 +0000
Subject: [PATCH] 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              |  7 ++++++-
 tst/testinstall/semigrp.tst | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/lib/semigrp.gi b/lib/semigrp.gi
index 509f37b601..ab837827bd 100644
--- a/lib/semigrp.gi
+++ b/lib/semigrp.gi
@@ -113,7 +113,12 @@ 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",
+InstallMethod(ViewString, "for an inverse semigroup with semigroup generators",
+[IsInverseSemigroup and HasGeneratorsOfSemigroup],
+_ViewStringForSemigroups);
+
+InstallMethod(ViewString, 
+"for an inverse semigroup with inverse semigroup generators",
 [IsInverseSemigroup and HasGeneratorsOfInverseSemigroup],
 _ViewStringForSemigroups);
 
diff --git a/tst/testinstall/semigrp.tst b/tst/testinstall/semigrp.tst
index fe48046fc7..ddb3014b4c 100644
--- a/tst/testinstall/semigrp.tst
+++ b/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);