proposition: Lemma length_update : forall l i v, length (l[i:=v]) = length l.
proof: Proof. Proof using. intros. unfold update_inst, update_impl, length, update. simpl. case_if. math. rewrite~ length_update. Qed.
imports: TLC(LibTactics LibLogic LibOperation LibReflect LibProd LibNat LibInt LibOption LibWf) TLC(LibInt)