%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-7-6 on page II-546 in "Indexing citations automatically".
%%
%% 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{105.0pt}

 %  Use biber program
 %% show second page

  \makeatletter
  \renewcommand\section{\@startsection{section}{1}{\z@}%
    {-1.25ex \@plus-1ex \@minus-.2ex}%
    {.5ex}%
    {\normalfont\normalsize\bfseries}}

% we need a trivial index environment with 1 column for the small example

  \renewenvironment{theindex}{\section*{\indexname}%
    \begin{flushleft}\let\item\@idxitem}{\end{flushleft}}

  \renewcommand\indexspace{\par}

  \makeatother

  \setlength\parindent{0pt}
  \setlength\parskip{0pt}

%StartShownPreambleCommands
\usepackage{makeidx}  \makeindex
\usepackage[indexing=cite]{biblatex} \addbibresource{tlc.bib}
\renewbibmacro{citeindex}{\ifciteindex{\indexnames{labelname}}{}}
%StopShownPreambleCommands

\begin{document}
\textcite{LGC97}, \textcite{Knuth-CT-a} % p.6 (not shown)
\newpage \printindex                    % p.7 (shown on the left)
\end{document}