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 Th304; :: thesis: verum