proposition: Lemma oppr_eq0 x : (- x == 0) = (x == 0).
proof: Proof. by rewrite (inv_eq opprK) oppr0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)