theorem
  for f, g being Function st x in dom f \ dom g holds (f \ g).x = f.x
proof
  let f, g be Function such that
A1: x in dom f \ dom g;
  f \ g c= f & dom f \ dom g c= dom (f \ g) by XTUPLE_0:25;
  hence thesis by A1,Th2;
end;
