proposition: Lemma enc_stack_spec R s t : s/t el R -> HFeq ⊢ opair (enc_string s) (enc_string t) ∈ enc_stack R.
proof: Proof. induction R as [|[u v] R IH]; cbn; auto. intros [[=]| H]; subst. - apply HF_bunion_el. apply DI2. apply HF_sing_el. - apply HF_bunion_el. apply DI1. now apply IH. Qed.
imports: Undecidability.FOL.ZF Undecidability.FOL.Syntax.Facts Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.Sets.ZF Undecidability.FOL.Reductions.PCPb_to_HF Undecidability.PCP(PCP Util.PCP_facts Reductions.PCPb_iff_dPCPb) Undecidability(Shared.ListAutomation)