
theorem Th16:
  for I be non empty set, G be Group,
      a be finite-support Function of I,G
  st a = I --> 1_G
  holds Product a = 1_G
  proof
    let I be non empty set, G be Group,
        a be finite-support Function of I,G;
    assume a = I --> 1_G; then
    support(a) is empty by Th12;
    hence thesis by Th15;
  end;
