proposition: Lemma CratP x : reflect (exists a, x = QtoC a) (x \in Crat).
proof: Proof. by apply: (iffP eqP) => [<- | [a ->]]; [exists (CtoQ x) | rewrite ratCK]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun ssrnat eqtype seq choice) mathcomp(div fintype path bigop finset prime order ssralg) mathcomp(poly polydiv mxpoly generic_quotient countalg) mathcomp(ssrnum closed_field ssrint archimedean rat intdiv) mathcomp(algebraics_fundamentals)