Elsevier cas-dc problem: minipage and "LaTeX Error: Command \bibsep already defined"

Question

In this question ( see Old question ) you talked about how to line up two figures with minipage in Elsevier cas-dc class. I had the same problem. I tried adding this patch, and now the code works correctly! However, this leads to a new error: "LaTeX Error: Command \bibsep already defined" ... How can I fix this? Thank you

This is a part of my code (I cannot put more for privacy reasons but at least the error appears):

\documentclass[a4paper,fleqn]{cas-dc}

\AddToHook{begindocument/before}{\ifdefined\bibsep\else\newlength\bibsep\fi} % class might be broken...

\ExplSyntaxOn
\exp_args:NNno \exp_args:Nno \use:n { \cs_gset:Npn 
\__make_fig_caption:nn #1#2 }
  {
\exp_after:wN \use_ii_i:nn \exp_after:wN
  { \__make_fig_caption:nn {#1} {#2} }
  { \dim_set:Nn \l_fig_width_dim \linewidth }
  }
\exp_args:NNno \exp_args:Nno \use:n { \cs_gset:Npn \__make_tbl_caption:nn #1#2 }
  {
\exp_after:wN \use_ii_i:nn \exp_after:wN
  { \__make_tbl_caption:nn {#1} {#2} }
  { \dim_set:Nn \l_tbl_width_dim \linewidth }
  }
\ExplSyntaxOff

\usepackage{natbib}

\usepackage{duckuments}


% If the frontmatter runs over more than one page
% use the longmktitle option.

%\documentclass[a4paper,fleqn,longmktitle]{cas-dc}

%\usepackage[numbers]{natbib}
%\usepackage[authoryear]{natbib}
\usepackage[authoryear,longnamesfirst]{natbib}
\usepackage{subcaption}

%%%Author macros
\def\tsc#1{\csdef{#1}{\textsc{\lowercase{#1}}\xspace}}
\tsc{WGM}
\tsc{QE}
%%%
\begin{document}
\let\WriteBookmarks\relax
\def\floatpagepagefraction{1}
\def\textpagefraction{.001}

% Short title
\shorttitle{...}    

% Short author
\shortauthors{...}  

% Main title of the paper
\title [mode = title]{....}

% Title footnote mark
% eg: \tnotemark[1]
\tnotemark[] 


% First author
%
% Options: Use if required
% eg: \author[1,3]{Author Name}[type=editor,
%       style=chinese,
%       auid=000,
%       bioid=1,
%       prefix=Sir,
%       orcid=0000-0000-0000-0000,
%       facebook=<facebook id>,
%       twitter=<twitter id>,
%       linkedin=<linkedin id>,
%       gplus=<gplus id>]

\author[1]{...}[]

% Corresponding author indication
\cormark[1]

% Footnote of the first author
\fnmark[]

% Email id of the first author
\ead{...}

% Address/affiliation
\affiliation[a]{
organization={University}}

\author[1]{...}[
]

% Footnote of the second author
\fnmark[]

% Corresponding author text
\cortext[1]{Corresponding author}



% For a title note without a number/mark
%\nonumnote{}

% Here goes the abstract
\begin{abstract}
...
\end{abstract}

% Keywords
% Each keyword is seperated by \sep
\begin{keywords}
...
\end{keywords}

\maketitle
% Main text

\section*{Appendix A}
\label{appendixA}
\renewcommand{\thefigure}{A.\arabic{figure}}
\setcounter{figure}{0}

\begin{figure*}
\centering
\begin{minipage}[t]{0.43\textwidth}
\centering
\includegraphics[width=\textwidth]{Figure Appendix/imageA.4.png}
\caption{....}
\end{minipage}
\qquad
\begin{minipage}[t]{0.43\textwidth}
\centering
\includegraphics[width=\textwidth]{Figure Appendix/imageA.5.png}
\caption{....}
\end{minipage}
\end{figure*}
\end{document}

Answer 1

My answer in to the other question unconditionally did a \newlength\bibsep as the class was missing that when I took a look at it. It might be that you got a version of it that doesn't have this flaw (but from my memory there were quite a few flaws in it, I doubt every one of those is fixed).

If you're loading a package like natbib that might provide a \bibsep as well and you might get an error because of that.

However, to (hopefully, I can't guarantee anything without an MWE showing where your problem is) fix this, you can check whether \bibsep is defined and if it isn't do the definition. I've put this into the begindocument/before hook where it should work (unless you got some packages loaded later than that, so no guarantee...):

\documentclass[]{cas-dc}

\AddToHook{begindocument/before}{\ifdefined\bibsep\else\newlength\bibsep\fi} % class might be broken...

\ExplSyntaxOn
\exp_args:NNno \exp_args:Nno \use:n { \cs_gset:Npn \__make_fig_caption:nn #1#2 }
  {
    \exp_after:wN \use_ii_i:nn \exp_after:wN
      { \__make_fig_caption:nn {#1} {#2} }
      { \dim_set:Nn \l_fig_width_dim \linewidth }
  }
\exp_args:NNno \exp_args:Nno \use:n { \cs_gset:Npn \__make_tbl_caption:nn #1#2 }
  {
    \exp_after:wN \use_ii_i:nn \exp_after:wN
      { \__make_tbl_caption:nn {#1} {#2} }
      { \dim_set:Nn \l_tbl_width_dim \linewidth }
  }
\ExplSyntaxOff

% just an example of a package defining `\bibsep`, `natbib` is not needed for the answer to work
\usepackage{natbib} % might be the culprit for you (poor package does nothing wrong)

% just some dummy contents for our MWE, not needed for the answer to work
\usepackage{duckuments}

\begin{document}
\blindduck[all]
\begin{figure*}
  \begin{minipage}[t]{0.48\linewidth}
    \includegraphics[width=\linewidth]{example-image-duck}
    \caption{Problems due to rivet aging\label{fig-problemofrivet}}
  \end{minipage}
  \hfill
  \begin{minipage}[t]{0.48\linewidth}
    \includegraphics[width=\linewidth]{example-image-duck}
    \caption{Example of rivet replacement by the bolt\label{fig-rivetrepla}}
  \end{minipage}
\end{figure*}
\blindduck[all]
\end{document}