fact: Fixpoint M_combinations B x y := match B with | nil => y = ∅ | (s,t)::B => exists y1 y2, M_is_bunion y2 y1 y /\ M_combinations B x y1 /\ M_is_rep (M_comb_rel s t) x y2 end.
imports: Undecidability.FOL.Syntax.Facts Undecidability.FOL.Semantics.Tarski.FullFacts Undecidability.FOL.FST Undecidability.FOL.Sets.FST Lia Undecidability.PCP(PCP Util.PCP_facts Reductions.PCPb_iff_dPCPb) Undecidability(Shared.ListAutomation)