Undecidability of QLTL and QCTL with two variables and one monadic predicate letter

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Mikhail Rybakov
Dmitry Shkatov

Abstract

We study the algorithmic properties of the quantified linear-time temporal logic QLTL in languages with restrictions on the number of individual variables as well as the number and arity of predicate letters. We prove that the satisfiability problem for QLTL in languages with two individual variables and one monadic predicate letter in Σ 11 -hard. Thus, QLTL is Π 11 -hard, and so not recursively enumerable, in such languages. The result
holds both for the increasing domain and the constant domain semantics and is obtained by reduction from a Σ 11 -hard N×N recurrent tiling problem. It follows from the proof for QLTL that similar results hold for the quantified branching-time temporal logic QCTL, and hence for the quantified alternating-time temporal logic QATL. The result presented in this paper strengthens a result by I. Hodkinson, F. Wolter, and M. Zakharyaschev, who have shown that the satisfiability problem for QLTL is Σ 11 -hard in languages with two individual variables
and an unlimited supply of monadic predicate letters.

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Section
Non-classical logics

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