proposition: Lemma sqrn_eq1 x : x <= 0 -> (x ^+ 2 == 1) = (x == -1).
proof: Proof. by rewrite -sqrrN -oppr_ge0 -eqr_oppLR => /sqrp_eq1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)