set A = KurExSet ;
Cl (Int KurExSet ) = Cl ((Cl (KurExSet ` )) ` ) by TOPS_1:def 1;
then A1: Int (Cl (Int KurExSet )) = (Cl ((Cl ((Cl (KurExSet ` )) ` )) ` )) ` by TOPS_1:def 1;
(Cl ((Cl (KurExSet ` )) ` )) ` = ].-infty ,4.[ by Th21, TOPMETR:24, XXREAL_1:224, XXREAL_1:294;
then Cl ((Cl ((Cl (KurExSet ` )) ` )) ` ) = ].-infty ,4.] by BORSUK_5:77;
hence Int (Cl (Int KurExSet )) = ].4,+infty .[ by A1, TOPMETR:24, XXREAL_1:224, XXREAL_1:288; :: thesis: verum