Factoring directed graphs with respect to the cardinal product in polynomial time II

By a result of McKenzie [7] all finite directed graphs that satisfy certain connectivity conditions have unique prime factorizations with respect to the cardinal product. McKenzie does not provide an algorithm, and even up to now no polynomial algorithm that factors all graphs satisfying McKenzie’s conditions is known. Only partial results [1, 3, 5] have been published, all of which depend on certain thinness conditions of the graphs to be factored. In this paper we weaken the thinness conditions and thus significantly extend the class of graphs for which the prime factorization can be found in polynomial time.