%%
%% The LaTeX Companion, 3ed
%%
%% Example 2-4-7 on page I-87 in "cleveref --- Cleverly formatted references".
%%
%% 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{195.0pt}


  \usepackage{amsmath,cleveref}

  \AtEndDocument{%     we place the equations at the document end so that
                 %     they do not show up in the book and take up unnecessary space
    \newpage
    \begin{align}
      a &= b \label{eq:a} \\
      b &< c \label{eq:b} \\
      c &< d \label{eq:c} \\
      d &< e \label{eq:d} \\
      a &< e \label{eq:e} \\
    \end{align}
  }

%StartShownPreambleCommands
% equations as before + 2 more
%StopShownPreambleCommands

\begin{document}
\Cref{eq:c,eq:b,eq:a,eq:d,eq:e} are sorted and
\cref{eq:c,eq:b,eq:a,eq:e} are sorted with a gap.
But compare these results with referencing
\cref{eq:c,,eq:b,eq:a,eq:d,eq:e}! Surprised?
\end{document}