sectioningsections-paragraphs
Very simple question:
Is \paragraph supposed to be used only under \subsubsection or do you use it directly under \section or \subsection as well (e.g., if there are no further sub sections necessary).
I mean, because you wouldn't use \subsubsection directly under \chapter …
Quoting the manual from the titlesec package:
With the help of classes you may insert, say, a new subchapter level between chapter and section, or creating a scheme of your own.
(at subsection 3.9 in the titlesec.pdf).
At appendix 9.2, it shows exactly how the already existing sections and the like are defined; don't copy the already existing parts to your file, but use them as inspiration for defining new ones (amount of indentation, style, etc). My advice is to look at all the appendices and subsection 3.9.
Use the first optional argument for \newtheorem:
\documentclass{book}
\usepackage{amsthm}
\newtheorem{theo}[subsubsection]{Theorem}
\newtheorem{defi}[subsubsection]{Definition}
\setcounter{secnumdepth}{3}
\begin{document}
\chapter{Test Chapter}
\section{Test Section}
\subsection{Test Subsection}
\subsubsection{Test Subsubsection}
\begin{theo}
test.
\end{theo}
\subsubsection{Test Subsubsection}
\begin{theo}
test.
\end{theo}
\begin{defi}
test.
\end{defi}
\subsubsection{Test Subsubsection}
\end{document}
I think this numbering schema can result hard to follow for readers (among other things, what if, for example, there's a theorem or a definition before a subsubsection is created?).
For the bonus point (and to make things even harder for the reader):
\documentclass{book}
\usepackage{amsthm}
\usepackage{amsmath}
\usepackage{etoolbox}
\numberwithin{equation}{subsection}
\newtheorem{theo}[subsubsection]{Theorem}
\newtheorem{defi}[subsubsection]{Definition}
\setcounter{secnumdepth}{3}
\AtBeginEnvironment{equation}{\setcounter{equation}{\value{subsubsection}}}{}{}{}
\AtEndEnvironment{equation}{\stepcounter{subsubsection}}{}{}{}
\begin{document}
\chapter{Test Chapter}
\section{Test Section}
\subsection{Test Subsection}
\subsubsection{Test Subsubsection}
\begin{theo}
test.
\end{theo}
\subsubsection{Test Subsubsection}
\begin{theo}
test.
\end{theo}
\begin{defi}
test.
\end{defi}
\begin{equation}
a=b.
\end{equation}
\subsubsection{Test Subsubsection}
\begin{equation}
c=d.
\end{equation}
\end{document}
I would rather use a simpler numbering schema:
\documentclass{book}
\usepackage{amsthm}
\usepackage{amsmath}
\newtheorem{theo}{Theorem}[chapter]
\newtheorem{defi}[theo]{Definition}
\newtheorem{prop}[theo]{Proposition}
\setcounter{secnumdepth}{3}
\begin{document}
...
\end{document}
Best Answer
Although not much bad happens in most cases if you break the rules, you should use
\paragraphbelow\subsubsection. Despite its rather unfortunate name\paragraphand\subparagraphare part of the section level hierarchy and unrelated to paragraphs of text.LaTeX is designed so that you can mark up sectional units and decide separately what level of sectioning is reflected in the table of contents, and what level is numbered.
If you set the counters
secnumdepthortocdepthabove 4 then you will bring in the paragraph level and the omitted subsubsection level 3 will be more obvious.