proposition: Lemma enc_derivations_step B n l : numeral l ∈ numeral n -> M_opair (σ (numeral l)) (M_enc_stack (derivations B (S l))) ∈ M_enc_derivations B n.
proof: Proof. Proof using M_ZF VIEQ. induction n; cbn -[derivations]. - now intros H % M_eset. - intros [H|H % sing_el] % binunion_el; apply binunion_el. + left. apply IHn, H. + right. apply numeral_inj in H as ->. now apply sing_el. Qed.
imports: Undecidability.FOL.ZF Undecidability.FOL.Syntax.Facts Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.Sets.ZF Lia Undecidability.PCP(PCP Util.PCP_facts Reductions.PCPb_iff_dPCPb) Undecidability(Shared.ListAutomation)