proposition: Lemma addNr : left_inverse zeroU oppU addU.
proof: Proof. by move=> x; apply: val_inj; rewrite !SubK addNr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)