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

theorem
  for p being Real holds
  [.-infty,+infty.[ \ ].p,s.[ = [.-infty,p.] \/ [.s,+infty.[
proof
  let p be Real;
  p in REAL by XREAL_0:def 1;
  hence thesis by Th325,XXREAL_0:9;
end;
