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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)
We introduce a new class of functions, called span functions which count the different output values that occur at the leaves of the computation tree associated with a nondeterministic polynomial time Turing machine transducer. This function class has natural complete problems; it is placed between Valiant's function classes # P and # NP, and contains both(More)
A polynomial time computable function ¦ £ ¦ £ whose range is a set Ä is called a proof system for Ä. In this setting, an-proof for Ü ¾ Ä is just a string Û with´Ûµ Ü. Cook and Reckhow defined this concept in [13], and in order to compare the relative strength of different proof systems for the set TAUT of tautologies in propositional logic, they considered(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 polynomialtime 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)
We introduce the class MP of languages L which can be solved in polynomial time with the additional information of one bit from a #P function f. We prove that the polynomial hierarchy and the classes Mod k P, k ≥ 2, are low for this class. We show that the middle bit of f (x) is as powerful as any other bit, and that a wide range of bits around the middle(More)