% 9-5-1.tex
\documentclass{article}
\begin{document}
\[
   a\ne0\ \bigg\{\begin{array}{l}b=0\ \Big\{\begin{array}{ll}c=0, & y=f(x),\\
   c\ne0, & y=g(x),\end{array}\\[7pt] b\ne0,\quad y=h(x). \end{array}
\]

\[\left(\begin{array}{cccc}
    a_{11} & a_{12} & \cdots & a_{1n}\\
           & a_{22} & \cdots & a_{2n}\\
           &        & \ddots & \vdots\\
    \multicolumn{2}{c}{\raisebox{1.3ex}[0pt]{\Huge0}} & & a_{nn}
  \end{array}\right)
\]

\newcommand*{\adots}{\mathinner{\mkern2mu\raisebox{0.1em}{.}
   \mkern2mu\raisebox{0.4em}{.}\mkern2mu\raisebox{0.7em}{.}\mkern1mu}}
\[
\begin{array}{c@{\hspace{-5pt}}l}
 \left(\begin{array}{ccc|ccc}
  a & \cdots & a & b & \cdots & b \\
    & \ddots & \vdots & \vdots & \adots \\
    &        & a      & b \\\hline
    & & & c & \cdots & c \\
    & & & \vdots & & \vdots \\
    \multicolumn{3}{c|}{\raisebox{2ex}[0pt]{\Huge0}}
    & c & \cdots & c
 \end{array}\right)
 & \begin{array}{l} \left.\rule{0mm}{7mm}\right\}p \\
   \\\left.\rule{0mm}{7mm}\right\}q
 \end{array} \\[-5pt]
 \begin{array}{cc} \underbrace{\rule{17mm}{0mm}}_m &
 \underbrace{\rule{17mm}{0mm}}_n \end{array} &
\end{array}
\]

$$
  \left(\begin{array}{lcr} lll & ccc & rrr \\
  l & c & r \end{array} \right) \eqno(5.3)
$$

\[
   A=\sum_{\mbox{\tiny $\begin{array}{c}
   1\le i\le m\\ 1\le j\le n\\ 1\le k\le p
   \end{array}$}} a_{ijk}
\]
\end{document}