J. Bang-Jensen and P. Hell, The e#ect of two cycles on the complexity of colorings by directed graphs, Discrete Applied Math. 26 (1990), 1-23.  Home/Search   Document Not in Database   Summary   Related Articles

....of H with the smallest number of edges, for which there is a homomorphism from H to K. We can clearly assume that the core does not contain isolated vertices. It is also easy to see that this notion is well defined in the sense that up to isomorphism the core is unique. We refer the reader to [10], 25] for more background and references on digraph homomorphisms, and to [24] for more information and references on cores of graphs. Our main result is the following precise characterization of the digraphs H for which testing PH with one sided error, has query complexity polynomial in 1 #. ....

J. Bang-Jensen and P. Hell, The e#ect of two cycles on the complexity of colorings by directed graphs, Discrete Applied Math. 26 (1990), 1-23.

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