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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)
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 show that the graph isomorphism problem is low for PP and for C = P, i.e., it does not provide a PP or C = P computation with any additional power when used as an oracle. Furthermore, we show that graph isomorphism belongs to the class LWPP (see Fenner, Fortnow, Kurtz [12]). A similar result holds for the (apparently more difficult) problem Group(More)
We i n vestigate 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 i n p o wer to #P and that ModP i s contained in the class AmpMP. As a consequence, the classes PP, ModP a n d AmpMP are all Turing equivalent, and thus AmpMP and ModP are not low(More)