\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amssymb}
\usepackage{textcomp}
\renewcommand{\text@accent}[3]{}
\newcommand{\zyva}[1]
{\texttt{\string#1} & #1{A}#1{a} & #1{E}#1{e} & #1{I}#1{\i} & #1{O}#1{o} &
#1{U}#1{u} & #1{Y}#1{y} & #1{C}#1{c} & #1{}}

\begin{document}

\section*{Text accent}
This table shows the accented letters that \hevea{} can generate.
\begin{tabular}{c@{\quad}*{8}{c}}
 & \textbf{Aa} &  \textbf{Ee} & \textbf{I\i} & \textbf{Oo} & \textbf{Uu}
 & \textbf{Yy} & \textbf{Cc} & --- \\
\hline
\zyva{\"}\\
\zyva{\'}\\
\zyva{\.}\\
\zyva{\=}\\
\zyva{\^}\\
\zyva{\`}\\
\zyva{\~}\\
\zyva{\b}\\
\zyva{\c}\\
\zyva{\k}\\
\zyva{\r}\\
\zyva{\u}\\
\zyva{\v}\\
\zyva{\H}\\
\zyva{\textcircled}
\hline
\end{tabular}

\section*{A few ``blackboard'' letters}
$$
\begin{array}{c}
\mathbb{CNRZQ}
\end{array}
$$

\end{document}
