theorem Th5:
  the_arity_of o = {} & Result(o,U0) <> {} implies const(o,U0) in Result(o,U0)
proof
  assume that
A1: the_arity_of o = {} and
A2: Result(o,U0) <> {};
  dom Den(o,U0) = Args(o,U0) by A2,FUNCT_2:def 1
    .= {{}} by A1,PRALG_2:4;
  then {} in dom Den(o,U0) by TARSKI:def 1;
  then Den(o,U0).{} in rng Den(o,U0) by FUNCT_1:def 3;
  hence thesis;
end;
