proposition: Lemma ler0_sqrtr a : a <= 0 -> sqrt a = 0.
proof: Proof. rewrite /sqrtr; case: (sig2W _) => x /= _. by have [//|_ /eqP//|->] := ltrgt0P a; rewrite mulf_eq0 orbb => /eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)