proposition: Lemma FST_bunion_unique T a b c c' : FSTeq <<= T -> T ⊢ is_bunion a b c -> T ⊢ is_bunion a b c' -> T ⊢ c ≡ c'.
proof: Proof. intros HT H1 H2. apply FST_ext'; trivial. - apply (FST_bunion_sub HT H1 H2). - apply (FST_bunion_sub HT H2 H1). Qed.
imports: Undecidability.FOL.Syntax.Facts Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.Deduction.FullNDFacts Undecidability.FOL.Sets.FST Undecidability.FOL.FST Undecidability.FOL.Reductions.PCPb_to_FST Undecidability.PCP(PCP Util.PCP_facts Reductions.PCPb_iff_dPCPb) Undecidability(Shared.ListAutomation)