Step 2 : write each vector | τ τ α α 1 i 2 [ 3.. N ] ⟩ ⟩ in terms of the at most (Vidal's emphasis) χ χ Schmidt vectors | Φ Φ α α 2 [ 3.. N ] ⟩ ⟩ and, correspondingly, coefficients λ λ α α 2 [ 2 ] : | τ τ α α 1 i 2 [ 3.. N ] ⟩ ⟩ = ∑ ∑ α α 2 Γ Γ α α 1 α α 2 [ 2 ] i 2 λ λ α α 2 [ 2 ] | Φ Φ α α 2 [ 3.. N ] ⟩ ⟩