reconsider B = {1}, C = ((RAT 2,4) \/ ].4,5.[) \/ ].5,+infty .[ as Subset of R^1 by TOPMETR:24;
set A = KurExSet ;
A1: KurExSet = {1} \/ (((RAT 2,4) \/ ].4,5.[) \/ ].5,+infty .[) by XBOOLE_1:113;
A2: B ` = ].-infty ,1.[ \/ ].1,+infty .[ by BORSUK_5:90;
C ` = ((].-infty ,2.] \/ (IRRAT 2,4)) \/ {4}) \/ {5} by BORSUK_5:89;
hence KurExSet ` = (((].-infty ,1.[ \/ ].1,2.]) \/ (IRRAT 2,4)) \/ {4}) \/ {5} by A1, A2, BORSUK_5:92, XBOOLE_1:53; :: thesis: verum