# Collection of papers with combine class: incompatibility with latex3/xparse

I'm trying to put together a collection of papers in a single edited volume with the combine class. This gives a series of errors, but none fatal, and typesetting is successful. However, some of the papers to be included in my volume use the package forest, and this causes a fatal error (TeX capacity exceeded, sorry [input stack size=5000].), and no typeset.

A minimal example for the master document looks like this:

\documentclass[11pt]{combine}
\usepackage{kantlipsum}
\usepackage{combinet} %toc at collection level
\usepackage{forest}

\title{A Collection of Papers}
\author{Collection editors}
\date{}

\begin{document}

\pagestyle{combine}
\maketitle
\tableofcontents
\clearpage

\begin{papers}
\label{article1}
\import{article1}
\end{papers}

\end{document}


And one for the paper that is to be included looks like this:

\documentclass[11pt]{article}
\usepackage{kantlipsum}

\title{The Noumena}
\author{I. Kant}
\date{}

\begin{document}

\maketitle

\kant[42]

\end{document}


As they are given here, the documents fail to typeset. Commenting out the forest package in the master document, however, results in a successful typeset.

EDIT: The conflict is due to the fact that forest loads xparse. Hence, it appears that this is a combine/LaTeX 3 incompatibility. See developer's comments on question.

• I get the same error, LaTeX error: "kernel/command-already-defined" Control sequence \__driver_color_pickup: already defined when trying to load xparse (which forest uses). So I guess the problem is between LaTeX3 and combine. – Sašo Živanović Nov 19 '17 at 18:17
• Related: tex.stackexchange.com/questions/395454/… @SašoŽivanović. – cfr Nov 20 '17 at 1:30
• Please leave the added latex3 tags! They were correctly added, then removed and I've now re-added. latex3/xparse is absolutely relevant here. – cfr Nov 20 '17 at 1:32
• Would the docmute package be an alternative solution here? The combine class is rather awkward. – Will Robertson Nov 20 '17 at 2:07
• @WillRobertson docmute does not generate a table of contents at the collection level based on the \title and \author fields of the individual papers, as far as I can see. – Guido Vanden Wyngaerd Nov 20 '17 at 21:14