theorem
  x is being_a_square & (y is being_a_sum_of_squares or y is
  being_a_product_of_squares or y is being_a_sum_of_products_of_squares or y is
being_an_amalgam_of_squares or y is being_a_sum_of_amalgams_of_squares or y is
generated_from_squares) implies x+y is generated_from_squares by Lm70,Lm71,Lm72
