
theorem Th3:
  for X being set, f being PartFunc of X,REAL,
  g being non-empty PartFunc of X,REAL holds dom(f/g) = dom f /\ dom g
proof
  let X be set, f be PartFunc of X,REAL, g be non-empty PartFunc of X,REAL;
  thus dom (f/g) = dom f /\ (dom g \ g"{0}) by RFUNCT_1:def 1
    .= dom f /\ dom g;
end;
