“…Let f be an assignment function that interprets the free variables of ϕ in the domain A of A. The semantic game G(A, f , ϕ) is played between the two players ∃ and ∀ in the usual way (see, e.g., [11,18]). If the verifying player ∃ has a winning strategy in the game G(A, f , ϕ), we write A, f |= + ϕ and say that ϕ is true in (A, f ).…”