Hi chat! I have a question about something in the proof of the formula of the determinant of a block lower triangular matrix in Huffman - Kunze.
Huffman and Kunze first show that if $B$ is obtained from $A$ by adding the rows $c\alpha_j$ to $\alpha_i$ where $i<j$ then $\det A=\det B$. Then they define $D(A,B,C)=\det\begin{bmatrix}
A & B \\ 0 & C
\end{bmatrix}$, if $A$ and $B$ are fixed then $D$ is alternating and $s$-linear as a function of the rows of $C$, so by a previous theorem $$D(A,B,C)=(\det C) D(A,B,I)$$ where $I$ is the identity function with $s\times s$ dimension. Now they claim t…