if it is logically equivalent to a formula of the form ∃ X 1 ⋯ ∃ X k ψ {\displaystyle \exists X_{1}\cdots \exists X_{k}\psi }
У той час як арыфметыка поўная адносна формул віду ∃ x 1 … ∃ x k ( P = Q ) {\displaystyle \exists x_{1}\dots \exists x_{k}(P=Q)}