%%
%% The LaTeX Companion, 3ed
%%
%% Example 6-6-2 on page I-468 in "boldline --- Bolder table rules".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{87.0pt}

%StartShownPreambleCommands
\usepackage{boldline}        \renewcommand\arraystretch{1.3}
\newcolumntype{I}{V{2.5}}    \newcommand\boldline{\hlineB{4}}
\newcommand\boldcline[1]{\clineB{#1}{4}}
%StopShownPreambleCommands

\begin{document}
\begin{tabular}{cIc|c}
  A &  B & C  \\ \cline{1-1} \boldcline{3-3}  a & b  & c \\ \hline
  X & Y & Z   \\ \boldline                  100 & 10 & 1
\end{tabular}
\end{document}