quick fix for the missing level in the holonomy when there is no singleton image

Author: egri-nagy

lib/skeleton.gi

@@ -295,7 +295,12 @@ end);
 InstallMethod(DepthOfSkeleton,
         "for a skeleton (SgpDec)", [IsSkeleton],
 function(sk)
-  return Maximum(Depths(sk));
+#quick fix for losing one level due to nonimage singletons
+  if Size(BaseSet(sk)) = Length(NonImageSingletons(sk)) then
+    return Maximum(Depths(sk)) + 1;
+  else
+    return Maximum(Depths(sk));
+  fi;
 end);
 
 #returns the representative element of the scc of a finiteset

tst/skeleton.tst

@@ -40,7 +40,7 @@ gap> ImageWitness(sk, FiniteSet([5]), FiniteSet([1..5]));
 #testing for a semigroup with no singleton image - they should not be reported in the depth
 gap> sk := Skeleton(Semigroup(Transformation([4,2,4,4])));;
 gap> DepthOfSkeleton(sk);
-2
+3
 gap> TilesOf(sk, FiniteSet([1,3],4));
 fail