let r be ext-real number ; :: thesis: for s being real number holds [.r,+infty .[ \ [.s,+infty .[ = [.r,s.[
let s be real number ; :: thesis: [.r,+infty .[ \ [.s,+infty .[ = [.r,s.[
s in REAL by XREAL_0:def 1;
then s < +infty by XXREAL_0:9;
hence [.r,+infty .[ \ [.s,+infty .[ = [.r,s.[ by Th194; :: thesis: verum