# Indentation in proof environment within description environment

I currently have

\documentclass[10pt]{article}
\usepackage[text={7.2in,9.6in}]{geometry}
\geometry{letterpaper}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}

\begin{document}
\begin{description}
\item[Problem 8~]
A woman starts at a point $P$.

\begin{proof}[Response]
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point
\end{proof}
\end{description}

\begin{proof}[Response]
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point
\end{proof}
\end{document}


which produces the following:

My goal is to have the second paragraph in the "response" in the proof environment within the description environment indented like it is outside of the description environment.

I imagine the problem may be in how I am using the geometry package, but I am unsure. Is there a way to have the second paragraph indented (and also no added white space) after a new line break in the proof environment within the description environment?

• by "indented like it is outside of the description environment", do you mean that you want the first line indented? (that seems more likely than that you want the paragraph, with initial indent, shoved all the way against the left margin.) Commented Sep 23, 2016 at 20:46
• @barbarabeeton I apologize--I realize my phrasing was hardly the cleanest. I want the indentation that occurs in the second instance of the duplicated text, where "If a point ... " actually is indented. I want that indentation in the example of the text produced above it where "If a point ... " is not indented and there is also vertical white space placed to mark the separation. I hope that makes my question clearer. Commented Sep 23, 2016 at 20:49
• I should maybe add that I have only placed the second instance of the duplicated text to illustrate that the description environment clearly introduces my "problem" (I, at least, see the lack of indentation after a new paragraph in the proof environment to be problematic). Commented Sep 23, 2016 at 20:52
• okay, description lists do change the shapes of paragraphs. looking in the file size10.clo (where the settings for a 10pt article reside), i see that \parindent=15pt. so if you put \parindent=15pt before that second paragraph, it will indent, and the indent should persist if you have more paragraphs. or in the preamble, you can insert \newdimen\normalparindent \normalparindent=\parindent and then you can use \parindent=\normalparindent whenever you need to reset to that value. (if that works for you, i can make this a proper answer.) Commented Sep 23, 2016 at 21:00
• @barbarabeeton That is great to know and it does persist with more paragraphs. The only thing that still perplexes me is why there is the increased white space between paragraphs. Does the description environment also add a certain amount of vertical white space between occurrences of paragraphs? For example, multiple occurrences of the dummy paragraph look like this. Commented Sep 23, 2016 at 21:05

No, geometry has no role in this. The problem is that proof uses internally trivlist, which inherits some of its parameters from the enclosing description environment.

You can define your own environment that restores the relevant parameters.

\documentclass[10pt]{article}
\usepackage[text={7.2in,9.6in}]{geometry}
\geometry{letterpaper}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}

\newlength{\normalparindent}
\newlength{\normalparskip}
\AtBeginDocument{%
\setlength{\normalparindent}{\parindent}%
\setlength{\normalparskip}{\parskip}%
}

\newenvironment{response}
{\proof[Response]%
\setlength{\parskip}{\normalparskip}%
\setlength{\parindent}{\normalparindent}}
{\endproof}

\begin{document}
\begin{description}
\item[Problem 8~]
A woman starts at a point $P$.

\begin{response}
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point
\end{response}
\end{description}

\begin{response}
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point
\end{response}
\end{document}


• That is great to know, especially for future use. Thanks for the great answer (as always)! Commented Sep 23, 2016 at 21:11

Or, use the enumitem package:

\documentclass[10pt]{article}
\usepackage[text={7.2in,9.6in}]{geometry}
\geometry{letterpaper}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{enumitem}

\begin{document}
\begin{description}[listparindent=\parindent,parsep=0pt]
\item[Problem 8~]
A woman starts at a point $P$.

\begin{proof}[Response]
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point\ldots

\end{proof}
\end{description}

\begin{proof}[Response]
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point
\end{proof}
\end{document}


For completeness’ sake, here is the output:

A better solution involves creating your custom “description-like” environment:

\documentclass[10pt]{article}
\usepackage[text={7.2in,9.6in}]{geometry}
\geometry{letterpaper}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{enumitem}

\newlist{DWRdescription}{description}{1} % <<< Increase last argument if you
%     need to nest "DWRdescription"
%     environments.
\setlist[DWRdescription]{listparindent=\parindent,parsep=0pt}

\begin{document}

\begin{DWRdescription}

\item[Problem 8~]
A woman starts at a point $P$.

\begin{proof}[Response]
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point\ldots

\end{proof}

\end{DWRdescription}

\begin{proof}[Response]
The north pole is such a point. And there are others:
Consider a point $a_1$ near the south pole such that
the parallel passing through $a_1$ forms a
circle $C_1$ with circumference exactly one mile.

If a point $a_2$ (or $a_3, a_4, \ldots$) is chosen
near the south pole so that the parallel passing
through it forms a circle $C_2$ ($C_3, C_4, \ldots$)
with a circumference of exactly $\frac{1}{2}$ mile
($\frac{1}{3}$ mile, $\frac{1}{4}$ mile, \ldots),
then the point
\end{proof}
\end{document}


The output should be exactly the same as before.