Does the graph isomorphism problem for directed graphs($GI_{di}$) reduce to the graph isomorphism problem for directed graphs($GI_{un}$)?
It is clear $$GI_{un}\leq GI_{di}$$ since the set of undirected graphs is subset of set of directed graphs. Does the converse hold true? That is, can an algorithm for undirected graphs used to test for problems in $GI_{di}$ with polynomial increase in complexity? Is $$GI_{di}\leq GI_{un}?$$