proposition: Lemma addr0_eq x y : x + y = 0 -> - x = y.
proof: Proof. by rewrite -[-x]addr0 => <-; rewrite addKr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)