reserve x for set,
  p,q,r,s,t,u for ExtReal,
  g for Real,
  a for Element of ExtREAL;

theorem Th329:
  p < q implies [.-infty,q.[ \ ].p,s.] = [.-infty,p.] \/ ].s,q.[
  by Th306,XXREAL_0:5;
