proposition: Lemma up_sshift2 (phi : form') sigma : phi[sshift 2][up (up (up sigma))] = phi[up sigma][sshift 2].
proof: Proof. rewrite !subst_comp. apply subst_ext. intros [|[]]; trivial. cbn. unfold funcomp. now destruct (sigma 0) as [|[]]. cbn. unfold funcomp. now destruct sigma as [|[]]. 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)