%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-4-11 on page II-168 in "Stacking in subscripts and superscripts".
%%
%% 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{tlc3examargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{81.0pt}

  % Shorten the vertical size of the example ...
  \AtBeginDocument{%
    \setlength\abovedisplayskip{.3\abovedisplayskip}%
    \setlength\belowdisplayskip{.3\belowdisplayskip}%
  }

%StartShownPreambleCommands
\usepackage{mathtools}
%StopShownPreambleCommands

\begin{document}
\[ \prod_{a^2<c} \quad
 \prod_{\begin{subarray}{l} a^2<c\\c<1 \end{subarray}} \quad
 \prod_{\begin{crampedsubarray}{l} a^2<c\\c<1 \end{crampedsubarray}} \]
\end{document}
