From cc93123387ea3681e8213e184082f9d815b3aca7 Mon Sep 17 00:00:00 2001
From: Alexander Hulpke <hulpke@math.colostate.edu>
Date: Thu, 26 Apr 2018 18:24:49 -0600
Subject: [PATCH] FIX: (partial) for #2400

1) Wrong `IsTrivial` set in empty submagma

2) Fix `Submagma` method by replacing the empty submagma with the one-submagma,
if it turns out a group. (Work around bug, not a fix)
---
 lib/addmagma.gi | 2 +-
 lib/magma.gi    | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/addmagma.gi b/lib/addmagma.gi
index 72f692d91b..ab653cbf46 100644
--- a/lib/addmagma.gi
+++ b/lib/addmagma.gi
@@ -175,7 +175,7 @@ InstallGlobalFunction( SubadditiveMagmaNC, function( M, gens )
     if IsEmpty( gens ) then
       K:= NewType( FamilyObj(M),
                        IsAdditiveMagma
-                   and IsTrivial
+                   and IsEmpty
                    and IsAttributeStoringRep );
       S:= Objectify( K, rec() );
       SetGeneratorsOfAdditiveMagma( S, [] );
diff --git a/lib/magma.gi b/lib/magma.gi
index 6c1eac9b3a..69a8f92851 100644
--- a/lib/magma.gi
+++ b/lib/magma.gi
@@ -1213,6 +1213,9 @@ InstallMethod( AsMagma,
     D := AsSSortedList( D );
     L := ShallowCopy( D );
     M := Submagma( MagmaByGenerators( D ), [] );
+    if IsGroup(M) then
+      M:=Submagma(MagmaByGenerators(D),[One(ElementsFamily(FamilyObj(D)))]);
+    fi;
     SubtractSet( L, AsSSortedList( M ) );
     while not IsEmpty(L)  do
         M := ClosureMagmaDefault( M, L[1] );