proposition: Lemma unitrN1 : -1 \is a @unit R.
proof: Proof. by apply/unitrP; exists (-1); rewrite mulrNN mulr1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)