proposition: Lemma addr_eq0 x y : (x + y == 0) = (x == - y).
proof: Proof. by rewrite -[y in LHS]opprK subr_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)