theorem
  x is being_a_sum_of_squares & y is being_a_sum_of_squares implies x*y
  is generated_from_squares
proof
  assume x is being_a_sum_of_squares & y is being_a_sum_of_squares;
  then x is generated_from_squares & y is generated_from_squares by Lm38;
  hence thesis by Lm87;
end;
