proposition: Lemma lem_isort_sortedb : forall l, sortedb (isort l).
proof: Proof. induction l; sauto use: lem_insert_sortedb. Qed.
imports: Hammer(Tactics) Arith ZArith List Lia Hammer(Hints) Reals Lra Hammer(Reflect) Nat Psatz String Relations Sorting.Permutation