Logical laws for existential monadic second-order sentences with infinite first-order parts

Abstract

We consider existential monadic second-order sentences ∃X φ(X) about undirected graphs, where ∃X is a finite sequence of monadic quantifiers and φ(X) ∈ +∞ωω is an infinite first-order formula. We prove that there exists a sentence (in the considered logic) with two monadic variables and two first-order variables such that the probability that it is true on G(n, p) does not converge. Moreover, such an example is also obtained for one monadic variable and three first-order variables.