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
  r <= s implies [.r,+infty.[ \ ].p,s.] = [.r,p.] \/ ].s,+infty.[
proof
  let p be Real;
  p in REAL by XREAL_0:def 1;
  hence thesis by Th306,XXREAL_0:9;
end;
