let X be set ; :: thesis: ( X in {(Cl KurExSet),(Cl (Int KurExSet)),(Cl (Int (Cl KurExSet)))} implies X <> REAL )
assume A1: X in {(Cl KurExSet),(Cl (Int KurExSet)),(Cl (Int (Cl KurExSet)))} ; :: thesis: X <> REAL
per cases ( X = Cl KurExSet or X = Cl (Int KurExSet) or X = Cl (Int (Cl KurExSet)) ) by A1, ENUMSET1:def 1;
end;