Determinantal inequalities for block triangular matrices
  Let $T=\begin{bmatrix} X &Y\\ 0 & Z\end{bmatrix}$ be an $n$-square matrix, where $X, Z$ are $r$-square and $(n-r)$-square, respectively. Among other determinantal inequalities, it is proved $\det(I_n+T^*T)\ge \det(I_r+X^*X)\cdot \det(I_{n-r}+Z^*Z)$ with equality holds if and only if $Y=0$. 
Minghua Lin
math.FA