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

theorem Th337:
  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;
  then -infty < s by XXREAL_0:12;
  hence thesis by Th305;
end;
