let p, q, s be ExtReal; :: thesis: ( p <= q implies [.-infty,q.[ \ [.p,s.[ = [.-infty,p.[ \/ [.s,q.[ )
-infty <= s by XXREAL_0:5;
hence ( p <= q implies [.-infty,q.[ \ [.p,s.[ = [.-infty,p.[ \/ [.s,q.[ ) by Th302; :: thesis: verum