proposition: Lemma truncK : {in nat_num, cancel trunc (GRing.natmul 1)}.
proof: Proof. by move=> x; rewrite natrE => /eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order ssralg poly ssrnum ssrint)