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.] \ {s} = ].r,s.[
proof
  assume r < s;
  then
A1: ].r,s.] = ].r,s.[ \/ {s} by Th132;
  not s in ].r,s.[ by Th4;
  hence thesis by A1,ZFMISC_1:117;
end;
