### How to create a `\subsubsubsection`

LaTeX's set of "sections" stops at the level of `\subsubsection`. This reflects a design decision by Lamport - for, after all, who can reasonably want a section with such huge strings of numbers in front of it?

In fact, LaTeX standard classes do define "sectioning" levels lower than `\subsubsection`, but they don't format them like sections (they're not numbered, and the text is run-in after the heading). These deeply inferior section commands are `\paragraph` and `\subparagraph`; you can (if you must) arrange that these two commands produce numbered headings, so that you can use them as `\subsubsubsection`s and lower.

The titlesec allows you to adjust the definitions of the sectioning macros, and it may be used to transform a `\paragraph`'s typesetting so that it looks like that of a `\section`.

If you want to program the change yourself, you'll find that the commands (`\section` all the way down to `\subparagraph`) are defined in terms of the internal `\@startsection` command, which takes 6 arguments. Before attempting this sort of work, you are well advised to read the LaTeX sources (ltsect.dtx in the LaTeX distribution) and the source of the standard packages (classes.dtx). The LaTeX companion discusses use of `\@startsection` for this sort of thing.

`LaTeX source`
  macros/latex/base.tar.gz
`titlesec.sty`
  macros/latex/contrib/supported/titlesec.tar.gz