1

I would like the text of a long theorem to be indented, so that the text of the second line starts exactly below the text of the first line (and not below the word "Theorem") like this:

Theorem 1: This is a long thoerem where I would like the text in the second
                    line to be indented.

Here is a small example, where the text is unfortunately not indented.

\documentclass{article}

\newtheorem{Theorem}{Theorem}

\begin{document}

\begin{Theorem}
This is a long thoerem where I would like the text in the second line to be indented.
\end{Theorem}

\end{document}

Does anyone have an idea how to solve this?

Update: Based on the answer of Werner and the corresponding comments below, I would like to extend the example as follows, where I also create a table of theorems as well as references to the theorems in the footer, which currently does not work with the solution provided by Werner:

\documentclass[8pt]{extbook}

\usepackage{amsthm}
\usepackage{enumitem}
\usepackage{fancyhdr}
\usepackage{titletoc}
\usepackage{tocloft}

\newtheoremstyle{TheoremStyle}{3pt}{3pt}{\bfseries}{}{\bfseries}{}{.5em}{\thmname{#1}\thmnumber{ #2} \addcontentsline{ToT}{section}{#1~\protect\numberline{#2}{#3}}}
\theoremstyle{TheoremStyle}
\newtheorem{Theorem}{Theorem}

\makeatletter

\newcommand\TableofTheorems{\chapter*{Table of Theorems}\@starttoc{ToT}}

\begin{document}

\TableofTheorems
\newpage

\pagestyle{fancy}
\fancyhead[RO]{Theorem \theTheorem}
\fancyhead[LE]{Theorem \theTheorem}

\section*{Chapter 1}
\addcontentsline{ToT}{chapter}{Chapter 1}

\begin{Theorem}[This is a long thoerem where I would like the text in the second line to be indented.]
This is a long thoerem where I would like the text in the second line to be indented.
\end{Theorem}

\newpage

\begin{Theorem}[This is another theorem.]
This is another theorem.
\end{Theorem}

\newpage

\begin{Theorem}[This is the third Theorem]
This is another theorem.
\end{Theorem}

\end{document}
3

Theorems are actually lists. You can use enumitem to format a list that is represented in the way you want, while tocloft aids in setting up content for the List of Theorems:

enter image description here

\documentclass{article}

\newtheorem{Theorem}{Theorem}% Original Theorem definition

\usepackage{enumitem,tocloft}

\newenvironment{MyTheorem}[1][]{%
  \def\theoremtocarg{#1}% Capture optional argument
  \begin{enumerate}[
    series=theoremlist, % Maintain unique counter
    resume=theoremlist, % Continue from previous counter
    align=left,
    leftmargin=*,
    label={\bfseries Theorem \arabic*},
    ref=\arabic*
  ]
    \item \itshape%
    \addcontentsline{tot}{theorem}{\protect\numberline{\theenumi}\ \theoremtocarg}% Add theorem to List of Theorems
}{%
  \end{enumerate}
}

\newlistof[section]{theorem}{tot}{List of Theorems}% Define List of Theorems
\renewcommand{\cfttottitlefont}{\Large\bfseries}% Default for \section

\begin{document}

\listoftheorem

\section{First section}

\begin{Theorem}
  This is a long theorem where I would like the text in the second line to be indented.
\end{Theorem}

\begin{MyTheorem}[First theorem]
  This is a long theorem where I would like the text in the second line to be indented.
\end{MyTheorem}

\begin{Theorem}
  This is a long theorem where I would like the text in the second line to be indented.
\end{Theorem}

\begin{MyTheorem}[Second theorem]
  This is a long theorem where I would like the text in the second line to be indented.
\end{MyTheorem}

\end{document}
  • The indenting works fine, but I get two other problems: – Jack Sep 13 at 19:45
  • @Jack: ...and they are? – Werner Sep 13 at 19:49
  • 1) I had created the following theoremstyle in order to add them to a table of theorems (ToT) - how can I do the exact same thing for such an environment: \newtheoremstyle{TheoremStyle}{3pt}{3pt}{\bfseries}{}{\bfseries}{}{.5em}{\thmname{#1}\thmnumber{ #2} \addcontentsline{ToT}{section}{#1~\protect\numberline{#2}{#3}}} \theoremstyle{TheoremStyle} 2) I referenced to the Theorems using \thetheorem (for example to write the number of the Theorem in the footer.) Is there a similar command for the Environment as well? – Jack Sep 13 at 19:53
  • 1
    @Jack: Can you supply a more complete, minimal example that replicates your current setup? What package do you use to employ \newtheoremstyle? You should really be up front about what you're using. – Werner Sep 13 at 19:57
  • See update above – Jack Sep 13 at 21:38

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