let s be real number ; :: thesis: [.s,+infty .] \ [.s,+infty .[ = {+infty }
s in REAL by XREAL_0:def 1;
then s < +infty by XXREAL_0:9;
hence [.s,+infty .] \ [.s,+infty .[ = {+infty } by Th401; :: thesis: verum