Curious TOC problem

David Carlisle d.p.carlisle at
Mon Apr 1 23:23:24 CEST 2019

The error message means you have `\addvspace`  in horizontal mode, the
fragment you show generates no error with the standard definitions


\contentsline {chapter}{Preface}{v}{section*.1}
\contentsline {section}{\numberline {1}Definition of category}{1}{section.1}
\contentsline {subsection}{\numberline {1.1}Some constructions for


But presumably you have definitions setting some level of the contents
"inline" as a paragraph rather than individual display lines, followed
by a display line that is expecting to be in vertical mode, without
ending the previous paragraph.

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