2 * m * n - m * n ^ 2 + m * n ^ 2 - m ^ 2 * n = 2 * m * n + m * n ^ 2
3 * a ^ 3 * b - a * b ^ 3 + a ^ 3 * b + a * b ^ 3 = 4 * a ^ 3 * b
2 * m * n - m * n ^ 2 + m * n ^ 2 - m ^ 2 * n = 2 * m * n + m * n ^ 2
3 * a ^ 3 * b - a * b ^ 3 + a ^ 3 * b + a * b ^ 3 = 4 * a ^ 3 * b