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

theorem Th331:
  p <= q implies [.-infty,q.[ \ [.p,s.] = [.-infty,p.[ \/ ].s,q.[
proof
  -infty <= s by XXREAL_0:5;
  hence thesis by Th310;
end;
