We introduce various kinds of fixed-point properties for modal logics, and we classify the most prominent systems according to these. Our goal is to do a first step towards a complete characterization of provability logics of (possibly non standard) derivability predicates for Peano Arithmetic.
We prove that for i ≥ 1, the arithmetic does not prove a variant of its own Herbrand consistency restricted to the terms of depth in , where ε is an arbitrarily small constant greater than zero. On the other hand, the provability holds for the set of terms of depths in .
According to the Furstenberg-Zimmer structure theorem, every measure-preserving system has a maximal distal factor, and is weak mixing relative to that factor. Furstenberg and Katznelson used this structural analysis of measure-preserving systems to provide a perspicuous proof of Szemerédi’s theorem. Beleznay and Foreman showed that, in general, the transfinite construction of the maximal distal factor of a separable measure-preserving system can extend arbitrarily far into the countable ordinals....
We study relations between propositional Monotone Sequent Calculus (MLK --- also known as Geometric Logic) and Resolution with respect to the complexity of proofs, namely to the concept of the polynomial simulation of proofs. We consider Resolution on sets of monochromatic clauses. We prove that there exists a polynomial simulation of proofs in MLK by intuitionistic proofs. We show a polynomial simulation between proofs from axioms in MLK and corresponding proofs of contradiction (refutations) in...
Continuing the earlier research [Fund. Math. 129 (1988) and 149 (1996)] we give some information about extending automorphisms of models of PA to cofinal extensions.