由已知, 存在可逆矩阵 P,Q 满足 P^-1AP = B, Q^-1CQ = D
令 H =
P 0
0 Q
则 H^-1 =
P^-1 0
0 Q^-1
且 H^-1 [ A 0; 0 C] H = [B 0; 0 D]