The Procrustean method of entanglement concentration can be used for as little as one partly entangled pair, being more efficient than the Schmidt projection method for entangling less than 5 pairs, and requires Alice and Bob to know the bias ( θ θ ) of the n pairs in advance. The method derives its name from Procrustes because it produces a perfectly entangled state by chopping off the extra probability associated with the larger term in the partial entanglement of the pure states: cos ⁡ ⁡ θ θ | ↑ ↑ A ⟩ ⊗ ⊗ | ↓ ↓ B ⟩ − − sin ⁡ ⁡ θ θ | ↓ ↓ A ⟩ ⊗ ⊗ | ↑ ↑ B ⟩