[Nauty] multigraphs

[Sterten at aol.com]

since Nauty can't yet handle multi-graphs, let's transform a multigraph  G
into a digraph G'.
Let the vertices of G' be the edges of G and there is  an edge
from vertex x to vertex y in G' , iff the target of edge x in  G
equals the source of edge y in G.
 
Now, is it true that multigraphs G and H are isomorphic,
iff their  derived digraphs G' and H' are isomorphic ?
 
Given the canonical form of G', how do we transfer it
back into a  canonical multigraph isomorphic to G ?
 

Guenter.
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