On the Logic of LGB Type Structures. Part II: Reentrancy Structures

Exact Complexity of the Satisfiability Problem for Strategy Logic

We show that the satisfiability problem for Strategy Logic introduced by Mogavero, Murano, and Vardi is $\Pi^1_\infty$-complete, and, more strongly, computably isomorphic to true second-order arithmetic. The lower bound is established for the next-time Boolean-goal fragment of Strategy Logic. Consequently, Strategy Log...

Gentzen systems and Beth tableaux

This paper provides an expository comparison of two foundational proof systems in classical propositional logic: Gentzen's sequent calculus and Beth's semantic tableaux. Gentzen's sequent calculus is presented as a rule-based system built upon the single axiom $\alpha \Rightarrow \alpha$, whose key feature — the subfor...

A Realizability Approach to Constructing Higher Types via Classifiers

On Recursion in Graded Modal Type Theory

We present a graded modal type theory with recursion over natural numbers and prove formally in Agda that it handles resources correctly, in the sense that an abstract machine accesses resources the “correct” number of times. The theory is parametrized, and can for instance be instantiated with grades for erasure, line...

Failure of Higher-Order Truth within Intuitionistic Propositional Logic

We answer the question whether all Heyting algebras can appear as the lattice of subterminal objects of an elementary topos in the negative. Concretely, we show that the free Heyting algebra on two generators, hence also on N generators for every N greater than 2, cannot be such a Heyting algebra. The mathematical resu...

GenZ: A Generic Sequent Calculus Prover using the Zipper

GenZ is introduced, a generic theorem prover for sequent calculi implemented in Haskell that allows the user to specify a set of sequent rules, over which it performs proof search, and employs the zipper data structure.