set A = KurExSet ;
( not 5 in {1} & not 5 in RAT (2,4) )
by BORSUK_5:29, 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 Th10, XBOOLE_0:def 3;
hence
Cl KurExSet <> KurExSet
by A1, XBOOLE_0:def 3; verum