proposition: Lemma minus_L1 : forall p q x, p>=q -> x+(p-q)=x+p-q.
proof: Proof. intros. apply Nle_plus in H. destruct H. rewrite H. rewrite (Nat.add_comm q) at 1. rewrite Nat.add_sub. rewrite Nat.add_assoc. replace (x+q+x0) with (q+(x+x0)). rewrite (Nat.add_comm q). rewrite Nat.add_sub. auto. ring. Qed.
imports: Coq(Arith Lia)