English

Craig interpolation theorem fails in bi-intuitionistic predicate logic

Logic 2024-05-29 v3

Abstract

In this article we show that bi-intuitionistic predicate logic lacks the Craig Interpolation Property. We proceed by adapting the counterexample given by Mints, Olkhovikov and Urquhart for intuitionistic predicate logic with constant domains (G. Mints, G. K. Olkhovikov and A. Urquhart. Failure of Interpolation in Constant Domain Intuitionistic Logic. Journal of Symbolic Logic, 78: 937--950 (2013)). More precisely, we show that there is a valid implication ϕψ\phi \rightarrow \psi with no interpolant (i.e. a formula θ\theta in the intersection of the vocabularies of ϕ\phi and ψ\psi such that both ϕθ\phi \rightarrow \theta and θψ\theta \rightarrow \psi are valid). Importantly, this result does not contradict the unfortunately named `Craig interpolation' theorem established by Rauszer in (Cecylia Rauszer. Craig Interpolation Theorem for an Extention of Intuitionistic Logic. Bull. Ac. Pol. Sc., 25(4), 337--341 (1977)) since that article is about the property more correctly named `deductive interpolation' (see Galatos, Jipsen, Kowalski and Ono's use of this term in N. Galatos, P. Jipsen, T. Kowalski, \& H. Ono. Residuated Lattices: An Algebraic Glimpse at Substructural Logics. Studies in Logic and the Foundations of Mathematics, Vol. 151. Amsterdam: Elsevier B. V. (2007)) for global consequence. Given that the deduction theorem fails for bi-intuitionistic logic with global consequence, the two formulations of the property are not equivalent.

Cite

@article{arxiv.2205.00245,
  title  = {Craig interpolation theorem fails in bi-intuitionistic predicate logic},
  author = {Grigory K. Olkhovikov and Guillermo Badia},
  journal= {arXiv preprint arXiv:2205.00245},
  year   = {2024}
}

Comments

23 pages, 0 figures

R2 v1 2026-06-24T11:03:26.760Z