9（a+1)^2(a-1)^2-6(a^2-1)(b^2-1)+(b+1)^2(b-1)^2
=[3(a^2-1)]^2-6(a^2-1)(b^2-1)+(b^2-1)^2
=(3a^2-3)^2-6(a^2-1)(b^2-1)+(b^2-1)^2
=[(3a^2-3)-(b^2-1)]^2
=(3a^2-b^2-2)^2