The sim-ThornGuide target merges all TeX documentation files and produces a single PDF file as output. This break is documentation.tex file use \newcommand to define (possibly conflicting commands). Pull request https://bitbucket.org/cactuscode/cactus/pull-requests/83/cactus-support-newcommand-in-documentation/diff encloses the extracted part in a \begingroup … \endgroup thus ensuring that commands are only locally defined for each thorn.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2321/allow-use-of-latex-newcommand-in-thorn