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We present a logspace algorithm that constructs a canonical intersection model for a given proper circular-arc graph, where canonical means that models of isomorphic graphs are equal. This implies that the recognition and the isomorphism problems for this class of graphs are solvable in logspace. For a broader class of concave-round graphs, that still(More)
This paper studies the class MP of languages which can be solved in polynomial time with the additional information of one bit from a #P function f. The middle bit of f (x) is shown to be as powerful as any other bit, whereas the O(log n) bits at either end are apparently weaker. The polynomial hierarchy and the classes Mod k P, k ≥ 2, are shown to be low(More)
We investigate the computational power of the new counting class ModP which generalizes the classes Mod p P, p prime. We show that ModP is polynomial-time truth-table equivalent in power to #P and that ModP is contained in the class AmpMP. As a consequence, the classes PP, ModP and AmpMP are all Turing equivalent, and thus AmpMP and ModP are not low for MP(More)
It is shown that the assumption of NP having polynomial-size circuits implies (apart from a collapse of the polynomial-time hierarchy as shown by Karp and Lip-ton) that the classes AM and MA of Babai's Arthur-Merlin hierarchy coincide. This means that also a certain inner collapse of the remaining classes of the polynomial-time hierarchy occurs. It is well(More)