fact: Definition preimage_class (aT rT : Type) (D : set aT) (f : aT -> rT) (G : set (set rT)) : set (set aT) := [set D `&` f @^-1` B | B in G].
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)