1

When I want to enumerate in the proof environment I usually use the command enumerate or \item[label].

The first one seems very nice as it counting automatically. However, it is also a trouble when I want, for example, to derive the proof of two part at the same time, and hence want to write something like (i-ii). Also, I don't like the way it aligned the text.

For the second one solved these two problems but there is one catch. If I use it at the beginning of the proof, it would start in a new line, not after the word Proof. Is there any way to fix this or is there anything I can do to improve the enumerate command. Here is my sample code

\documentclass[11pt,a4paper]{article}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{graphicx}
\newtheorem{thm}{Theorem}
\begin{document}

    \begin{thm}
        The following statements are true
        \begin{enumerate}
            \item 
            \label{thm:1}
            $1+1=2$;
            \item 
            \label{thm:2}
            $2+2=4$;
        \end{enumerate}
    \end{thm}
    \begin{proof}
        In order to divide the proof into two parts, I use \emph{enumerate}
        \begin{enumerate}
            \item This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

            This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

            \item This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

            This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.
        \end{enumerate}
        Or \emph{item} with label option
        \item[\ref{thm:1}.] 
        This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

        This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

        \item[\ref{thm:2}.] 
        This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

        This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.
    \end{proof}

    I prefer the second one as it can deal with the case when I want to combine the proof. However, it has one drawback that it can only start at the begining of a line.

    \begin{proof}
        \item[\ref{thm:1} - \ref{thm:2}] For \emph{item} with label option.
    \end{proof}
    \begin{proof}
        \begin{enumerate}
            \item \emph{enumerate} \qedhere
        \end{enumerate}
    \end{proof}

\end{document}

and the result looks like this

enter image description here

  • I find that long indented proofs are only a waste of space. Just issue \medspace (or even nothing) between parts and use the label (with proper indentation) at the start of the next paragraph. – egreg Nov 11 '17 at 21:41
1

For the second case, I suggest defining a clone of the description environment, conveniently customised with the enumitem package. Similarly, for the first case a colne of enumerate. So I defined a proofenum and a proofdescr environments. I also changed the input encoding to utf8:

\documentclass[11pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[showframe]{geometry}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{graphicx}
\usepackage{enumitem}

\newtheorem{thm}{Theorem}

\newlist{proofenum}{enumerate}{1}
\setlist[proofenum]{label=\arabic*., wide=0pt, leftmargin=*}
\newlist{proofdescr}{description}{1}
\setlist[proofdescr]{font=\normalfont, leftmargin=0pt, style=sameline}

\begin{document}

\begin{thm}
    The following statements are true
    \begin{enumerate}
        \item
        \label{thm:1}
        $1+1=2$;
        \item
        \label{thm:2}
        $2+2=4$;
    \end{enumerate}
\end{thm}
\begin{proof}
    In order to divide the proof into two parts, I use \emph{enumerate}
    \begin{proofenum}
        \item This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

        This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

        \item This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

        This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.
    \end{proofenum}
    Or \emph{item} with label option
\begin{proofdescr}
    \item[\ref{thm:1}.]
    This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

    This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

    \item[\ref{thm:2}.]
    This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.

    This is a very very very very very very very very very very very very very very very very very very very very very very very very very very very very long proof.
\end{proofdescr}
\end{proof}

I prefer the second one as it can deal with the case when I want to combine the proof. However, it has one drawback that it can only start at the beginning of a line.

\begin{proof}
\begin{proofdescr}
    \item[\ref{thm:1} - \ref{thm:2}] For \emph{item} with label option.
    \item[\ref{thm:1} - \ref{thm:2}] For \emph{item} with label option.
\end{proofdescr}
\end{proof}
\begin{proof}
    \begin{proofenum}
        \item \emph{enumerate}
        \item \emph{enumerate}\qedhere
    \end{proofenum}
\end{proof}

\end{document} 

enter image description here

  • many thanks @Bernard . latin1 is just a mistake, I often use utf8x :p – mortal Nov 11 '17 at 21:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.