# Indenting all lines in a theorem environment

I have made the following theorem environment

\documentclass{article}

\usepackage{amsmath}
\usepackage{amsthm}

\newtheoremstyle{proposition}
{.5\baselineskip}
{.5\baselineskip}
{}                              % body
{}                              % indentation
{}{}
\theoremstyle{proposition}
\newtheorem{prop}{}

\begin{document}

\begin{prop}
Necessarily if there is life on the Evening Star then
there is life on the Evening Star.
\end{prop}

\end{document}


But now the second line is aligned with the ''head'' rather than the beginning of the text. Can that be changed?

Also, is it possible to make the indentation fixed relative to the left margin rather than the end of the head (which may vary in width)?

I'd like something similar to the following

This seems quite like the original:

\documentclass[a4paper]{article}
\usepackage[textwidth=275pt]{geometry}
\usepackage{microtype}
\usepackage{enumitem}

\newlist{thminner}{enumerate}{1}
\setlist[thminner]{
label=(\arabic*),
ref=\arabic*,
leftmargin=3em,
labelwidth=*,
topsep=\smallskipamount,
partopsep=0pt,
itemsep=0pt,
align=left,
resume,
}
\newenvironment{thm}{\thminner\item}{\endthminner}

\AtBeginDocument{\setlength{\parindent}{1.5em}}
\frenchspacing

\begin{document}

% this is just to get the first real theorem to be numbered 14
\begin{thm}\setcounter{thminneri}{14}\end{thm}
\newpage

It will next be shown that referential opacity afflicts also
the so-called \emph{modal} contexts Necessarily~\dots' and
Possibly~\dots', at least when those are given the sense of
\emph{strict} necessity and possibility as in Lewis's modal
logic.\footnote{Lewis [1],\dots}
According to the strict sense of necessarily' and possibly',
these statements would be regarded as true:
\begin{thm}\label{9gt7}
$9$ is necessarily greater than $7$,
\end{thm}
\begin{thm}
Necessarily if there is life on the Evening Star then there
is life on the Evening Star,
\end{thm}
\begin{thm}
The number of planets is possibly less than~$7$,
\end{thm}
and these as false:
\begin{thm}
The number of planets is necessarily greater than~$7$,
\end{thm}
\begin{thm}
Necessarily if there is life on the Evening Star then there
is life on the Morning Star,
\end{thm}
\begin{thm}
$9$ is possibly less than $7$.
\end{thm}
The general idea of strict modalities…

\end{document}


I suggest using instead a custom enumerate-like environment. It uses a very simple code with enumitem:

\documentclass{article}

\usepackage{enumitem}

\newlist{myprop}{enumerate}{1}%
\setlist[myprop]{label =(\arabic*), resume, wide=0pt, leftmargin=*}

\usepackage{lipsum}

\begin{document}

\begin{myprop}
\item Necessarily if there is life on the Evening Star then
there is life on the Evening Star. Necessarily if there is life on the Evening Star then
there is life on the Evening Star.
\item \label{prop:2}Necessarily if there is life on the Evening Star then
there is life on the Evening Star. Necessarily if there is life on the Evening Star then
there is life on the Evening Star.
\end{myprop}
\lipsum[11]
\begin{myprop}
\item \label{prop:3}Necessarily if there is life on the Evening Star then
there is life on the Evening Star. Necessarily if there is life on the Evening Star then
there is life on the Evening Star.
\end{myprop}

From propositions \ref{prop:2} and \ref{prop:3}, we see that …

\end{document}


Edit (22-05):

If you don't want to type type item each time, you caan replace the above code with

 \newenvironment{myprop}%
{\enumerate[label=(\arabic*), resume, wide=0pt, labelwidth=\dimexpr 2cm-\labelsep, leftmargin=2cm]\item }%
{\endenumerate}

• thanks! is there a way to increase the indentation (leaving the label at the margin)? – Toothrot May 18 '19 at 21:50
• wide=0pt will always leave the label at the margin. For the indentation, you can set leftmargin to another value (* corresponds to the default label width+ \labelsep). – Bernard May 18 '19 at 21:54
• this doesn't affect the first line – Toothrot May 18 '19 at 22:01
• When the counter has more digits, you have to compensate, which will require some trial and error. I suggest this instead, supposing you want a left margin at 2em: wide=0pt, leftmargin=2em, labelwidth=\dimexpr 2em-\labelsep\relax – Bernard May 18 '19 at 22:35
• Please see my edit for this. – Bernard May 22 '19 at 19:21