proposition: Lemma sqrCK x : 0 <= x -> sqrtC (x ^+ 2) = x.
proof: Proof. exact: exprCK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)