proposition: Lemma eq_sshift2 (phi : form') t : phi[sshift 2][up (up t..)] = phi[sshift 1].
proof: Proof. erewrite subst_comp, subst_ext; try reflexivity. now intros [|]. Qed.
imports: Undecidability.FOL.ZF Undecidability.FOL.Syntax.Facts Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.Sets(minZF ZF) Undecidability.FOL.Sets.ZF Undecidability.FOL.Reductions.PCPb_to_ZF Undecidability(Shared.ListAutomation)