$$
\newcommand{\div}[4]{
\begin{array}{r|l}
#1 & #2\\
\hline
\begin{array}[t]{r}#4\end{array} & \begin{array}[t]{l}#3\end{array}
\end{array}
}

\newcommand{\matp}[3]{
\begin{array}{cc}
& #2 \\
#1 & #3
\end{array}
}

\newcommand{\R}{\mathbb{R}}
\newcommand{\C}{\mathbb{C}}
\newcommand{\N}{\mathbb{N}}
\newcommand{\Z}{\mathbb{Z}}
$$