proposition: Lemma erestrict0 : (cst 0 : T -> \bar R) \_ D = cst 0.
proof: Proof. by apply/funext => x; rewrite /patch/=; case: ifP. 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