theorem
  a|^3-b|^3 = (a-b)*((a+b)*(a+b)+a|^2+b|^2)/2
  proof
    A1: a|^2 - b|^2 = (a-b)*(a+b) by Th1;
    a|^3 - b|^3 = a|^(2+1)-b|^(2+1)
    .=(a-b)*((a+b)*(a+b)+a|^2+b|^2)/2 by A1,Th14;
    hence thesis;
  end;
