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;
  then -infty < r by XXREAL_0:12;
  hence thesis by Th47;
end;
