let r be ExtReal; :: thesis: for s being Real holds [.r,+infty.[ \ [.s,+infty.[ = [.r,s.[
let s be Real; :: thesis: [.r,+infty.[ \ [.s,+infty.[ = [.r,s.[
s in REAL by XREAL_0:def 1;
hence [.r,+infty.[ \ [.s,+infty.[ = [.r,s.[ by Th194, XXREAL_0:9; :: thesis: verum