Automatic subsection enumeration

Question

For our math lectures I have been hard-coding paragraphs like

\paragraph*{Definition 1.1.1 (foo)}
\paragraph*{Example 1.1.2}
\paragraph*{Proposition 1.1.3}

and I want to create new commands like \definition, \lemma, \theorem, ... which create such paragraphs and handle the numbering. Every command is nested in a subsection, if you need to know.

Any specific idea what would be the best?

Answer 1

No no no.

\setcounter{secnumdepth}{5} should make your paragraphs automatically have numbers.

Wait, rereading the question, the ntheorem package allows you to create new environments (not commands) that are automatically numbered and so on. This might be better.

Here's a quick example of how these things would work:

\documentclass{article}
\usepackage{ntheorem}
\newtheorem{theorem}{Theorem}[subsection]
\newtheorem{example}{Example}[subsection]
\begin{document}
\section{Foo}

\subsection{First sub}

\begin{theorem}
  Here is a theorem
\end{theorem}
\begin{theorem}
  Another theorem
\end{theorem}

\subsection{Second sub}
\begin{example}
  An example
\end{example}
\begin{theorem}
  A third theorem
\end{theorem}
\end{document}

Declaring a new theorem involves giving the environment a name, then giving the theorem type a name that will display and finally (optinally) tell it where it gets its numbering from. In this case, I have told both theorem and example to get their numbering from the subsection they sit in, but you can change that if you'd like.

Answer 2

You could use your own environment, something like the following:

\documentclass{article}

\newcounter{definition}[section] % counter will reset every section
\renewcommand{\thedefinition}{\thesubsection.\arabic{definition}}
\newenvironment{definition}{\refstepcounter{definition}{\bfseries Definition \thedefinition}}{}
\begin{document}

\section{foo}

\subsection{bar}

\begin{definition}\label{testmylabel}
Here is a definition.
\end{definition}

We see in \ref{testmylabel}.
\end{document}

Note that by using \refstepcounter you get the ability to use \label and \ref. If you plan to load any other theorem packages (such as ntheorem), you might like to use a different name for the definition, something like, 'mydefinition', to avoid potential clashes.

Below is a versatile environment you requested

\documentclass{article}
\usepackage{ifthen}

\newcounter{definition}[section]
\renewcommand{\thedefinition}{\thesubsection.\arabic{definition}}
\newenvironment{definition}{\refstepcounter{definition}{\bfseries Definition \thedefinition}}{}

\newenvironment{flexible}[1]{\refstepcounter{definition}%
\ifthenelse{\equal{#1}{def}}%
{%
    {\bfseries Definition \thedefinition}%
}%
{%
\ifthenelse{\equal{#1}{prop}}%
{%
    {\bfseries Proposition \thedefinition}%
}{}%
}%
}%
{} 
\begin{document}

\section{foo}

\subsection{bar}

\begin{definition}\label{testmylabel}
Here is a definition.
\end{definition}

We see in \ref{testmylabel}.

\begin{flexible}{def}
some text
\end{flexible}

\begin{flexible}{prop}
some text
\end{flexible}

\end{document}