proposition: Lemma join1'_neq0 (X : L') : join1' X != set0 :> set _.
proof: Proof. rewrite hull_eq0 set0P. case/set0P: (neset_neq0 X) => y. case/set0P: (neset_neq0 y) => x yx sy. exists x; exists y => //. rewrite -in_setE in sy. by rewrite sy. 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