proposition: Lemma sqrtrP a : sqrtr_spec a a (0 <= a) (a < 0) (sqrt a).
proof: Proof. have [a_ge0|a_lt0] := ger0P a. by rewrite -{1 2}[a]sqr_sqrtr //; constructor. by rewrite ltr0_sqrtr //; constructor. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)