# How to prove that there are only 2 classes in 3 qubits entangled state?

Given 2 non-biseparable classes of 3 qubits (more generally tripartite) entangled states :

1. $$|GHZ\rangle = \frac{1}{\sqrt{2}} \left(|000\rangle + |111\rangle\right)$$
2. $$|W\rangle = \frac{1}{\sqrt{3}} \left(|001\rangle + |010\rangle + |100\rangle \right)$$

I have no clue from the beginning to prove that there are only these 2 classes of 3 qubits entangled states. What I know is that these classes can't be transformed into each other by LOCC or Local-quantum operations, and the fact that these classes are the only maximally entangled states in 3 qubits. Is it impossible to find another class in 3 qubits?