proposition: Lemma fdistC12E x : fdistC12 x = P (x.1.2, x.1.1, x.2).
proof: Proof. case: x => -[b a] c; rewrite /fdistC12 fdistmapE /= -/(f (a, b, c)). by rewrite (big_pred1_inj inj_f). Qed.
imports: mathcomp(all_ssreflect ssralg fingroup perm matrix) mathcomp(all_algebra vector reals normedtype) mathcomp(mathcomp_extra boolp) mathcomp(Rstruct) ssrR logb realType_ext ssr_ext ssralg_ext bigop_ext