\frac{dx}{dt} \amp = x^2 - 4x - y + 4 \amp \frac{dy}{dt} \amp = x^3 - y \amp\amp x, y\text{ version} \frac{dw}{dt} \amp = z^3 - w \amp \frac{dz}{dt} \amp = z^2 - 4z - w + 4 \amp\amp z, w\text{ version}