BGL: out_degree requirement

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-01-11 12:05:07

I notice that out_degree is a requirement for IncidenceGraph, one of the
most-basic useful graph concepts, but that it's only used in isomorphism()
and minimum_degree_ordering(). Since finding the out_degree can be a burden
for heuristic searches of spaces which aren't represented in memory, I think
this restriction should be lifted in most places, e.g. for
breadth_first_visit().

-Dave

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