From 0918d9756392fe76a055a27cccc5b5b789429d19 Mon Sep 17 00:00:00 2001
From: Wilf Wilson <wilf@wilf-wilson.net>
Date: Wed, 13 Sep 2017 16:56:58 +0100
Subject: [PATCH] semigrp.gi: add One to GeneratorsOfMagma if needed

Resolves #371
---
 gap/semigroups/semigrp.gi |  4 ++--
 tst/testinstall.tst       | 11 +++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/gap/semigroups/semigrp.gi b/gap/semigroups/semigrp.gi
index b2a13dc415..a4fa578ac6 100644
--- a/gap/semigroups/semigrp.gi
+++ b/gap/semigroups/semigrp.gi
@@ -277,10 +277,10 @@ function(gens, opts)
 
   S := Objectify(NewType(FamilyObj(gens), filts), rec(opts := opts));
 
-  if CanEasilyCompareElements(gens) and not One(gens) in gens then
+  if not CanEasilyCompareElements(gens) or not One(gens) in gens then
     SetGeneratorsOfMagma(S, Concatenation([One(gens)], gens));
   else
-    SetGeneratorsOfMagma(S, AsList(gens));
+    SetGeneratorsOfMagma(S, gens);
   fi;
   SetGeneratorsOfMagmaWithOne(S, AsList(mgens));
 
diff --git a/tst/testinstall.tst b/tst/testinstall.tst
index 41d4dc8db7..9c8e9ce5b6 100644
--- a/tst/testinstall.tst
+++ b/tst/testinstall.tst
@@ -1656,6 +1656,17 @@ gap> S := SingularFactorisableDualSymmetricInverseMonoid(3);
 gap> IsMonoidAsSemigroup(S);
 false
 
+#T# Issue 371: GeneratorsOfSemigroup for a monoid
+gap> R := ReesMatrixSemigroup(Group(()), [[()]]);;
+gap> S := MonoidByAdjoiningIdentity(R);
+<commutative monoid with 1 generator>
+gap> GeneratorsOfSemigroup(S);
+[ ONE, (1,(),1) ]
+gap> Size(S);
+2
+gap> Elements(S);
+[ ONE, (1,(),1) ]
+
 #T# SEMIGROUPS_UnbindVariables
 gap> Unbind(B);
 gap> Unbind(D);