The \addcontentsline command adds an entry to the specified list or
- file is the extension of the file on which information is to be
written: toc (table of contents), lof (list of figures), or lot
(list of tables).
- sec_unit controls the formatting of the entry. It should be one
of the following, depending upon the value of the file argument:
- toc the name of the sectional unit, such as part or
- lof figure
- lot table
- entry is the text of the entry.