set A = KurExSet ;
( not 5 in {1} & not 5 in RAT 2,4 )
by BORSUK_5:52, TARSKI:def 1;
then
( not 5 in ].4,5.[ & not 5 in {1} \/ (RAT 2,4) )
by XBOOLE_0:def 3, XXREAL_1:4;
then A1:
( not 5 in ].5,+infty .[ & not 5 in ({1} \/ (RAT 2,4)) \/ ].4,5.[ )
by XBOOLE_0:def 3, XXREAL_1:235;
5 in [.2,+infty .[
by XXREAL_1:236;
then
5 in Cl KurExSet
by Th12, XBOOLE_0:def 3;
hence
Cl KurExSet <> KurExSet
by A1, XBOOLE_0:def 3; verum