fact: Variables k1 k2 : R.-sfker X ~> Y.
imports: HB(structures) mathcomp(all_ssreflect ssralg ssrnum ssrint interval finmap) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality fsbigop) reals ereal signed topology normedtype sequences esum measure numfun lebesgue_measure lebesgue_integral