DigraphMaximalQuotients (UpToIsomorphism) #896
Description
We can compute a quotient of a digraph, as defined in QuotientDigraph, by effectively merging two vertices and combining any appropriate edges.
Issue #593 has been stale for a long time, and @james-d-mitchell and I were just talking about what exactly it means. We decided on a smaller problem that would be more well defined and achievable without too much trouble:
DigraphMaximalQuotients(D) should take a digraph D and return a set of all the quotients that can be obtained from it by merging two vertices together – called its maximal quotients. This should be a set in which all entries are unique up to isomorphism, and possibly the attribute should be called DigraphMaximalQuotientsUpToIsomorphism.
To do things up to isomorphism, we could start by finding the automorphism group of D and using it somehow.