proposition: Lemma indic0 : \1_(@set0 T) = cst (0 : R).
proof: Proof. by apply/funext=> x; rewrite indicE in_set0. Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg ssrnum ssrint interval finmap) mathcomp(mathcomp_extra boolp classical_sets fsbigop) mathcomp(functions cardinality set_interval) signed reals ereal topology normedtype sequences