proposition: Theorem undecidable_entailment_ZF' : (exists V (M : interp V), extensional M /\ standard M /\ forall rho psi, In psi ZF' -> rho ⊨ psi) -> undecidable entailment_ZF'.
proof: Proof. intros H. apply (undecidability_from_reducibility PCPb_undec). exists solvable. now apply PCPb_entailment_ZF'. Qed.
imports: Undecidability.Synthetic.Definitions Undecidability.Synthetic.Undecidability Undecidability.FOL(Semantics.Tarski.FullFacts Semantics.Tarski.FullSoundness) Undecidability.FOL.Sets.Models(Aczel_CE Aczel_TD ZF_model HF_model) Undecidability.FOL.Reductions(ZF_to_HF PCPb_to_HF PCPb_to_HFD PCPb_to_ZFeq PCPb_to_ZF PCPb_to_ZFD) Undecidability.FOL.Sets.ZF Undecidability.FOL.ZF Undecidability.PCP(PCP PCP_undec Util.PCP_facts Reductions.PCPb_iff_dPCPb)