proposition: Lemma sqrr_sign n : ((-1) ^+ n) ^+ 2 = 1 :> R.
proof: Proof. by rewrite exprAC sqrrN !expr1n. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)