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

theorem
  r <= s implies [.r,s.] \ {r} = ].r,s.]
proof
  assume r <= s;
  then
A1: [.r,s.] = {r} \/ ].r,s.] by Th130;
  not r in ].r,s.] by Th2;
  hence thesis by A1,ZFMISC_1:117;
end;
