proposition: Lemma pre_op_neq0 X : pre_op X != set0 :> set _.
proof: Proof. by rewrite hull_eq0 neset_neq0. Qed.
imports: HB(structures) Reals mathcomp(all_ssreflect ssralg ssrnum) mathcomp(mathcomp_extra boolp classical_sets Rstruct reals) mathcomp(finmap) Reals_ext realType_ext classical_sets_ext ssrR fdist fsdist convex