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

theorem Th225:
  ].p,q.[ c= REAL
proof
  let x be ExtReal;
  assume
A1: x in ].p,q.[;
  then
A2: p < x by Th4;
  x < q by A1,Th4;
  hence thesis by A2,XXREAL_0:48;
end;
