(a^3 - a^2 - a + 1)/(a^3 - 3a^2 + 3a - 1)
=(a²-1)(a-1)/[(a³-1)-3a(a-1)]
=(a-1)²(a+1)/[(a-1)(a²-2a+1)
=(a-1)²(a+1)/[(a-1)³]
=(a+1)/(a-1)