proposition: Proposition nat_add_sub_eq (n : nat) {k: nat} : (k <= n) -> k + (n - k) = n.
proof: Proof. intro H. destruct (symmetric_paths _ _ (nataddsub_assoc k H)); destruct (nat_add_comm n k); exact (add_n_sub_n_eq _ _). Defined.
imports: Basics Spaces.Nat.Core