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 Th313; :: thesis: verum