Merge pull request #769 from james-d-mitchell/fix-is-full-trans-semi

Fix bug in IsFullTransformationSemigroup
gap-system · May 3, 2016 · c42598e · c42598e
2 parents cd4afab + 99ec2b0
commit c42598e
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Showing 2 changed files with 33 additions and 3 deletions.
diff --git a/lib/semitran.gi b/lib/semitran.gi
@@ -214,13 +214,16 @@ InstallMethod(IsFullTransformationSemigroup, "for a transformation semigroup",
 [IsTransformationSemigroup],
 function(s)
   local n, t;
+
+  n := DegreeOfTransformationSemigroup(s);
 
-  n:=DegreeOfTransformationSemigroup(s);
-  if HasSize(s) then
+  if n = 0 and HasIsTrivial(s) and IsTrivial(s) then 
+    return true;
+  elif HasSize(s) then
     return Size(s)=n^n;
   fi;
 
-  t:=FullTransformationSemigroup(n);
+  t:=FullTransformationSemigroup(DegreeOfTransformationSemigroup(s));
   return ForAll(GeneratorsOfSemigroup(t), x-> x in s);
 end);
 

diff --git a/tst/testinstall/semitrans.tst b/tst/testinstall/semitrans.tst
@@ -0,0 +1,27 @@
+#############################################################################
+##
+#W  semitrans.tst
+#Y  James D. Mitchell
+##
+#############################################################################
+##
+
+#
+gap> START_TEST("trans.tst");
+gap> display := UserPreference("TransformationDisplayLimit");;
+gap> notation := UserPreference("NotationForTransformations");;
+gap> SetUserPreference("TransformationDisplayLimit", 100);;
+gap> SetUserPreference("NotationForTransformations", "input");;
+
+# Test IsFullTransformationSemigroup in trivial cases
+gap> IsFullTransformationSemigroup(Semigroup(Transformation([1])));
+true
+gap> IsFullTransformationSemigroup(Semigroup(Transformation([1, 1])));
+false
+
+#
+gap> SetUserPreference("TransformationDisplayLimit", display);;
+gap> SetUserPreference("NotationForTransformations", notation);;
+
+#
+gap> STOP_TEST("trans.tst", 74170000);