proposition: Lemma negative_setU nu N M : nu.-negative_set N -> nu.-negative_set M -> nu.-negative_set (N `|` M).
proof: Proof. move=> nN nM; rewrite -bigcup2E; apply: bigcup_negative_set => -[//|[//|/= _]]. exact: negative_set0. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum ssrint interval) mathcomp(finmap fingroup perm rat) mathcomp(mathcomp_extra boolp classical_sets cardinality) mathcomp(functions fsbigop set_interval) HB(structures) reals ereal signed topology numfun normedtype sequences esum measure realfun lebesgue_measure lebesgue_integral