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

theorem
  for r being Real
  holds ].r,+infty.] \ [.p,+infty.[ = ].r,p.[ \/ {+infty}
proof
  let r be Real;
  r in REAL by XREAL_0:def 1;
  then r < +infty by XXREAL_0:9;
  hence thesis by Th319,XXREAL_0:3;
end;
