2

I want to have my theorem environments to enumerate using both numbers and letters. Right now I have this:

\documentclass{article}
\usepackage{amsthm}
\newtheorem{theorem}{Theorem}[section]
\begin{document}
\setcounter{section}{1}
\begin{theorem}
    This enumerates as ``1.1." but I want ``1.1.a."
\end{theorem}
\begin{theorem}
    Then this one would be ``1.1.b"
\end{theorem}
\end{document}

I know I can use

\renewcommand*{\thetheorem}{\alph{theorem}}

to enumerate with letters but I'm not sure how to proceed in applying that to this situation.

4
  • The other 1 refer to what?
    – Bernard
    May 22, 2018 at 16:39
  • 1
    @Bernard a subsection May 22, 2018 at 16:41
  • And if there's a section but no subsection yet when the theorem is enunciated?
    – Bernard
    May 22, 2018 at 16:42
  • so it I change it to \newtheorem{theorem}{Theorem}[subsection] I can get 1.1.1, but how would I get the lettering? May 22, 2018 at 16:45

1 Answer 1

1

If you want to prefix the section and subsection numbers to the theorem "number" (here: lowercase letter), you need to replace \newtheorem{theorem}{Theorem}[section] with \newtheorem{theorem}{Theorem}[subsection].

enter image description here

\documentclass{article}
\usepackage{amsthm} % for '\newtheorem' macro
\newtheorem{theorem}{Theorem}[subsection]
\renewcommand\thetheorem{\thesubsection.\alph{theorem}}

\begin{document}
\setcounter{section}{1}
\setcounter{subsection}{1}

\begin{theorem}
    I want ``1.1.a.'' -- check!
\end{theorem}
\begin{theorem}
    This one should be ``1.1.b.'' -- check!
\end{theorem}
\end{document}
2
  • If I start a new subsection afterwards, the letter enumeration does not reset. So, after setcounter{subsection}{2}, the next theorem is numbered 1.2.c rather than resetting to 1.2.a May 22, 2018 at 17:51
  • @CrimsonRain - \setcounter{subsection}{2} will definitely not give you the desired result -- but that's not because of any mistake in the code I posted. In fact, \setcounter{subsection}{2}, \stepcounter{subsection}, and \addtocounter{subsection}{1} will all fail to increment the theorem "slave counter". What you need to do is execute \refstepcounter{subsection} -- or, probably more simply, issue a \subsection{...} instruction.
    – Mico
    May 22, 2018 at 20:07

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