Changes requested by Meike

gap/PolygonalComplexes/discs.gi

@@ -148,7 +148,7 @@ InstallMethod( AllSimplicialSurfacesByEssentialButterflyInsertion,
 
         allp := __SIMPLICIAL_AllEssentialTwoPaths(surf);
 
-        surfaces := List(allp, t-> ButterflyInsertionSurface(surf, t)[1]);
+        surfaces := List(allp, t-> ButterflyInsertion(surf, t)[1]);
 
 
         return IsomorphismRepresentatives(surfaces);

gap/PolygonalComplexes/modification.gd

@@ -1581,10 +1581,11 @@ DeclareOperation("SplitAllVertices", [IsPolygonalComplex]);
 #! butterfly along a edge-path of length 2. The edge-path is given either
 #! as a list of three vertices such that these three vertices determine two
 #! edges of <A>surface</A>, meeting in the middle vertex, or as a list
-#! of two adjacend edges, or as a vertex-edge-path. The operation
+#! of two adjacent edges, or as a vertex-edge path. The operation
 #! <E>ButterflyInsertionSurface</E> can be viewed as splitting
 #! the middle vertex of the given vertex-edge path in <A>surface</A> into
-#! two new vertices.
+#! two new vertices. The inner edge of the butterfly will be inserted such
+#! that it is adjacent to the new vertices created by splitting the middle vertex.
 #!
 #! The function returns a list, where the first entry is the enlarged surface
 #! <A>newSurface</A> which has two faces more than the input surface. The
@@ -1598,7 +1599,7 @@ DeclareOperation("SplitAllVertices", [IsPolygonalComplex]);
 #! gap> disc := SimplicialUmbrella(5);
 #! simplicial surface (6 vertices, 10 edges, and 5 faces)
 #! gap> t:= [1,2,6];;
-#! gap> discbig:=ButterflyInsertionSurface(disc,t)[1];
+#! gap> discbig:=ButterflyInsertion(disc,t)[1];
 #! simplicial surface (7 vertices, 13 edges, and 7 faces)
 #! gap> CounterOfVertices(discbig);  
 #! counter of vertices ([ 2, 3, 6 ] degrees, and [ 3, 3, 1 ] multiplicities)
@@ -1623,11 +1624,11 @@ DeclareOperation("SplitAllVertices", [IsPolygonalComplex]);
 #! <Alt Only = "Text">
 #! Image omitted in terminal text
 #! </Alt>
-#! @Returns a pair, where the first entry is a surface and the second entry is the vertex edgepath encoding changes to the input surface.
+#! @Returns a pair, where the first entry is a surface and the second entry is the vertex-edge path encoding changes to the input surface.
 #! @Arguments surface, list
-DeclareOperation( "ButterflyInsertionSurface", [IsSimplicialSurface, IsList] );
+DeclareOperation( "ButterflyInsertion", [IsSimplicialSurface, IsList] );
 #! @Arguments surface, vertex-edge-path
-DeclareOperation( "ButterflyInsertionSurface", [IsSimplicialSurface, IsVertexEdgePath] );
+DeclareOperation( "ButterflyInsertion", [IsSimplicialSurface, IsVertexEdgePath] );
 #! @EndGroup
 
 

gap/PolygonalComplexes/modification.gi

@@ -1879,7 +1879,7 @@ InstallMethod( SplitAllVertices, "for a polygonal complex",
 );
 RedispatchOnCondition( SplitAllVertices, true, [IsTwistedPolygonalComplex], [IsPolygonalComplex], 0 );
 
-InstallMethod( ButterflyInsertionSurface,
+InstallMethod( ButterflyInsertion,
 "for a simplicial surface and a pair of edges or a vertex list", [IsSimplicialSurface,IsList],
 
      function( surface, t )
@@ -1892,10 +1892,11 @@ InstallMethod( ButterflyInsertionSurface,
         Length(CommonVerticesOfEdgesNC(surface,t[1],t[2])) = 0 then
           ErrorNoReturn("Requires a  pair of adjacent edges");
         fi;
-       t := Union(VerticesOfEdge(surface,t[1]),VerticesOfEdge(surface,t[2]));
-       if not t[2]  in CommonVerticesOfEdgesNC(surface,t[1],t[2]) then
+        edges := t;
+        t := Union(VerticesOfEdge(surface,t[1]),VerticesOfEdge(surface,t[2]));
+        if not t[2]  in CommonVerticesOfEdgesNC(surface,edges[1],edgest[2]) then
            w := t[2]; t[2] := t[1]; t[1] := w;
-       fi;
+        fi;
     elif Length(t) = 3 then
        # we expect a vertex path of length 3
        if not IsSubset(Vertices(surface),t) or
@@ -1939,8 +1940,8 @@ InstallMethod( ButterflyInsertionSurface,
 	i := First([1..3] , x-> Length(e[x][1])=1 and edges[1] in e[x][2] );
         Assert(0,i<>fail,"incorrect path");
 	# now e[i] is a single edge, corresponding to first in the path
+	# w is set to the first vertex in the path to be split
 	w := t[1];
-#        w := CommonVerticesOfEdgesNC(surface,edges[1],edges[2])[1];
         # find the other vertex of the image of w in the image edge 
         newverts := [];
         newverts[1] := OtherVertexOfEdgeNC(newSurface,
@@ -2007,12 +2008,12 @@ InstallMethod( ButterflyInsertionSurface,
 end
 );
 
-InstallMethod( ButterflyInsertionSurface,
+InstallMethod( ButterflyInsertion,
 "for a simplicial surface and vertex-edge path", [IsSimplicialSurface,IsVertexEdgePath],
 
      function( surface, t )
 
-     return ButterflyInsertionSurface( surface, VerticesAsList(t));
+     return ButterflyInsertion( surface, VerticesAsList(t));
 
 end
 );