proposition: Fact nat_sorted_cons_inv x ll : nat_sorted (x::ll) -> nat_sorted ll.
proof: Proof. intros H l a m b r ?; apply (H (x::l) _ m _ r); subst; solve list eq. Qed.
imports: List Arith Max Lia Wellfounded Bool Eqdep_dec Undecidability.Shared.Libs.DLW.Utils(list_focus utils_tac utils_list)