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 st s <= q holds [.r,s.] c= ].-infty,q.]
proof
  let r be Real;
  r in REAL by XREAL_0:def 1;
  hence thesis by Th39,XXREAL_0:12;
end;
