set A = KurExSet ;
5 in [.2,+infty .[ by XXREAL_1:236;
then A1: 5 in Cl KurExSet by Th12, XBOOLE_0:def 3;
A2: not 5 in ].4,5.[ by XXREAL_1:4;
A3: not 5 in ].5,+infty .[ by XXREAL_1:235;
( not 5 in {1} & not 5 in RAT 2,4 ) by BORSUK_5:52, TARSKI:def 1;
then not 5 in {1} \/ (RAT 2,4) by XBOOLE_0:def 3;
then not 5 in ({1} \/ (RAT 2,4)) \/ ].4,5.[ by A2, XBOOLE_0:def 3;
hence Cl KurExSet <> KurExSet by A1, A3, XBOOLE_0:def 3; :: thesis: verum