Ricerc@Sapienza

Cutting planes proofs for integer programs can naturally be defined both in a syntactic and in a semantic fashion. Filmus et al. (STACS 2016) proved that semantic cutting planes proofs may be exponentially stronger than syntactic ones, even if they use the semantic rule only once. We show that when semantic cutting planes proofs are restricted to have coefficients bounded by a function growing slowly enough, syntactic cutting planes can simulate them efficiently.

In this note we show two results about k-DNF resolution. First we prove that there are CNF formulas which require exponential length refutations in resolution extended with parities of size k, but have polynomial length refutations in k-DNF resolution. Then we show that small proofs in tree-like k-DNF resolution and narrow proofs in dag-like resolution have the same proving power, over CNFs. This latter result is clearly implicit in Krajíček (1994) [24] but this direct proof is focused on resolution and provides information about refutation width.

We show the close connection between the enumeration of cliques in a k-clique free graph G and the length of tree-like resolution refutations for formula Clique(G,k), which claims that G has a k-clique. The length of any such tree-like refutation is within a "fixed parameter tractable" factor from the number of cliques in the graph. We then proceed to drastically simplify the proofs of the lower bounds for the length of tree-like resolution refutations of Clique(G,k) shown in [Beyersdorff et at. 2013, Lauria et al. 2017], which now reduce to a simple estimate of the number of cliques.