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

theorem Th338:
  for s being Real holds p <= q
  implies ].-infty,q.] \ ].p,s.] = ].-infty,p.] \/ ].s,q.]
proof
  let s be Real;
  s in REAL by XREAL_0:def 1;
  hence thesis by Th307,XXREAL_0:12;
end;
