proposition: Fact lequiv_swap x y l : x::y::l ≃ₛ y::x::l.
proof: Proof. split; apply incl_cons; simpl; auto. Qed.
imports: Arith Lia List Permutation Undecidability.Shared.Libs.DLW.Utils(utils_tac php) Undecidability.Shared.Libs.DLW.Wf(measure_ind)