Matrix A defined above is matrix with eigenvalues 0 , 1 , i . It is easy to see that 1 ∈ ∈ Λ Λ ⊗ ⊗ ( A ) and i ∈ ∈ Λ Λ ⊗ ⊗ ( A ) , but ( 1 + i ) / 2 ∉ Λ Λ ⊗ ⊗ ( A ) . Actually, by direct computation we have Λ Λ ⊗ ⊗ ( A ) = { x + y i : 0 ≤ ≤ x , 0 ≤ ≤ y , x + y ≤ ≤ 1 } .