proposition: Lemma summableN D f : summable D f = summable D (\- f).
proof: Proof. by rewrite /summable; congr (_ < +oo); apply: eq_esum => t Dt; rewrite abseN. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum finmap) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality fsbigop) reals ereal signed topology sequences normedtype numfun