proposition: Lemma lem_sorted_concat_2 {A} {dto : DecTotalOrder A} : forall (l l1 l2 : list A) x y, Permutation l (x :: l1 ++ l2) -> Sorted (x :: l1) -> leb y x -> Sorted (y :: l2) -> Sorted l -> Sorted (y :: l).
proof: Proof. intros. rewrite lem_lelst_sorted in *. sauto db: lelst inv: -. Qed.
imports: Hammer(Tactics) Hammer(Reflect) Arith Lia Sorting.Permutation Program