ANEW RELATION‐COMBINING THEOREM AND ITS APPLICATION
Zhi‐Wei Sun · Mathematical logic quarterly · 1992
Abstract Let ∃n denote the set of all formulas ∃x1…∃xn[P(x1, …,xn) = 0], where P is a polynomial with integer coefficients. We prove a new relation‐combining theorem from which it follows that if ∃n is undecidable over N, then ∃2n+2 is undecidable over Z.