Suppose X = (X₁, X₂, X₃, X₄)^T has a multivariate normal N₄(0, I₂ ⊗ Σ), where I₂ is the 2 × 2 identity matrix, ⊗ is the Kronecker product, and Σ = \(\left[\begin{array}{cc}2 & -1 \\ -1 & 2\end{array}\right]\). Define Z = \(\left(\begin{array}{ll} \rm X_1 & \rm X_2 \\ \rm X_3 & \rm X_4\end{array}\right)\) and Q = ((Q_ij)) = Z^TZ. Suppose \(\rm χ_n^2\) denotes a chi-square random variate with n degrees of freedom, and W_m(n, Σ) denotes a Wishart distribution of order m with parameters n and Σ. The distribution of (Q₁₁ + Q₁₂ + Q₂₁ + Q₂₂) is