let p, q be ExtReal; :: thesis: ( p <= q implies [.-infty,q.] \ {p} = [.-infty,p.[ \/ ].p,q.] )
-infty <= p by XXREAL_0:5;
hence ( p <= q implies [.-infty,q.] \ {p} = [.-infty,p.[ \/ ].p,q.] ) by Th316; :: thesis: verum