Theorem Numbering problem - Lettered subsections

I am trying to write theorems that will number based on section and subsection.

I know this is the default when you enter, for example:

\newtheorem{defn}{Definition}[subsection]


but when I do this, it only shows the subsection, not the section. I think this may be because I have renamed my subsections to be lettered instead of numbered with the command:

\renewcommand\thesubsection{\Alph{subsection}}


My sections are numbered (1, 2, 3, etc.) and my subsections are lettered (A, B, C, etc.) When I use the \newtheorem command I get:

Definition A.1 instead of Definition 1.A.1

Any idea why it is dropping the section number and how to fix? (I am using the amsart document class)

• It would be really helpful to have a compilable document, not just fragments. Are you really using amsart? – user31729 May 17 '16 at 15:53
• maybe you should be using \numberwithin{section}{chapter}. – barbara beeton May 17 '16 at 15:56

Is this what is requested?

The redefinition of \thesubsection as {\Alph{subsection}} strips the section information of course from \thesubsection.

\thedefn is using \thesubsection.\arabic{defn} due to its definition, so \thesection is missing then.

\documentclass{amsart}

\newtheorem{defn}{Definition}[subsection]

\renewcommand\thesubsection{\Alph{subsection}}

\renewcommand{\thedefn}{\thesection.\thesubsection.\arabic{defn}}

\begin{document}

\section{Foo}

\subsection{Foo subsection}

\begin{defn}
Foo
\end{defn}

\end{document}

• This is exactly the answer I was looking for. Thank you! Much appreciated. – hp_ May 18 '16 at 15:18