Cannot compile ebooks-master\daishu-2\src\units\ds2-ch5-6.tex

[yilyu]

The error part is:
\begin{align*}
& \bm{\arg a = 0,} \
& \bm{\arg(-a) = \pi,} \
& \bm{\arg(a,i) = \dfrac{\pi}{2},} \
& \bm{\arg(-a,i) = \dfrac{3\pi}{2} \text{。}}
\end{align*}

Thanks a lot for your efforts in latexifying the classic textbooks!

[yilyu]

I replace \dfrac with \frac, this file can be compiled successfully.