proposition: Lemma naddr_eq0 (x y : R) : x <= 0 -> y <= 0 -> (x + y == 0) = (x == 0) && (y == 0).
proof: Proof. by move=> lex0 ley0; rewrite -oppr_eq0 opprD paddr_eq0 ?oppr_cp0 // !oppr_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)