Constraints, MMSNP and expander relational structures

Authors:
Gábor Kun
Affiliations:
Department of Algebra and Number Theory, Eötvös University, Budapest, Hungary
Venue:
Combinatorica
Year:
2013

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Abstract

We give a poly-time construction for a combinatorial classic known as Sparse Incomparability Lemma, studied by Erd驴s, Lovász, Nešetřil, Rödl and others: We show that every Constraint Satisfaction Problem is poly-time equivalent to its restriction to structures with large girth. This implies that the complexity classes CSP and Monotone Monadic Strict NP introduced by Feder and Vardi are computationally equivalent. The technical novelty of the paper is a concept of expander relations and a new type of product for relational structures: a generalization of the zig-zag product, the twisted product.