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An exponential separation between the parity principle and the pigeonhole principle. (English) Zbl 0866.03029

Summary: The combinatorial parity principle states that there is no perfect matching on an odd number of vertices. This principle generalizes the pigeonhole principle, which states that for a fixed bipartition of the vertices, there is no perfect matching between them. Therefore, it follows from recent lower bounds for the pigeonhole principle that the parity principle requires exponential-size bounded-depth Frege proofs. M. Ajtai [Feasible mathematics, Proc. Math. Sci. Inst. Workshop, Ithaka/NY (USA) 1989, Prog. Comput. Sci. Appl. Log. 9, 1-24 (1990; Zbl 0781.03045)] previously showed that the parity principle does not have polynomial-size bounded-depth Frege proofs even with the pigeonhole principle as an axiom schema. His proof utilizes nonstandard model theory and is nonconstructive. We improve Ajtai’s lower bound from barely superpolynomial to exponential and eliminate the nonstandard model theory. Our lower bound is also related to the inherent complexity of particular search classes [C. H. Papadimitriou, Combinatorics, graphs and complexity, Proc. 4th Czech. Symp., Prachatice/Czech. 1990, Ann. Discrete Math. 51, 245-250 (1992; Zbl 0798.68058)]. In particular, oracle separations between the complexity classes PPA and PPAD, and between PPA and PPP also follow from our techniques [the authors et al., “The complexity of NP search problems”, Proc. 27th Ann. ACM Symp. Theory of Computing, Las Vegas/NV (USA), 303-314 (1995)].

MSC:

03F20 Complexity of proofs
68Q15 Complexity classes (hierarchies, relations among complexity classes, etc.)
68Q25 Analysis of algorithms and problem complexity
Full Text: DOI

References:

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