fact: Definition ess_sup f := ereal_inf (EFin @` [set r | mu (f @^-1` `]r, +oo[) = 0]).
imports: mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality fsbigop ) reals ereal signed topology normedtype sequences esum numfun HB(structures)