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$\left|\begin{array}{cccc}
1 & b_1 & 0 & 0 \\
-1 & 1-b_1 & b_2 & 0 \\
0 & -1 & 1-b_2 & b_3 \\
0 & 0 & -1 & 1-b_3
\end{array}\right|=$
                        
不再提醒