proposition: Lemma enum_box_skew_uniq : uniq enum_box_skew.
proof: Proof. Proof using. apply: allpairs_uniq_dep => [|i _|]; try exact: iota_uniq. by move=> [r c] [r' c'] /= _ _ [<-{r'} <-{c'}]. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype