我会参考已经做过的练习，比如
练习 1（作者 [number]，第 i 章，练习 ij）
\documentclass[a4paper, 11pt, notitlepage]{report}
\usepackage{amsfonts} % if you want blackboard bold symbols e.g. for real numbers
\usepackage{graphicx} % if you want to include jpeg or pdf pictures
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{float}
\newtheorem{thm}{Theorem}[section]
\newtheorem{lem}[thm]{Lemma}
\newtheorem{prop}[thm]{Proposition}
\newtheorem{cor}[thm]{Corollary}
\newtheorem{Def}[thm]{Definition}
\newtheorem{cond}[thm]{Condition}
\newtheorem{rem}[thm]{Remark}
\newtheorem{conj}[]{Conjecture}
\newtheorem*{post}{Postulate 1}
\newtheorem*{post2}{Postulate 2}
\newtheorem{ex}{Exercise}
\newtheorem{exa}[thm]{Example}
\title{BLANK} % change this
\author{BLANK} % change this
\date{\today} % change this
\numberwithin{equation}{section}
\newcommand{\mres}{\mathbin{\vrule height 1.6ex depth 0pt width
0.13ex\vrule height 0.13ex depth 0pt width 1.3ex}}
\DeclareMathOperator{\proj}{proj}
\begin{document}
\begin{ex}
Let $F_1, F_2, \dots$ be $1$-sets in the plane such that $F =
\end{ex}
\begin{proof}
If all the $F_i$'s are regular, each $F_i$ may be covered by a countable union of
rectifiable curves except for a set of zero measure. Thus $\bigcup_{i=1}^{\infty}F_i$
may be covered by a countable union of rectifiable curves, except for a countable of
zero measure sets; thus by positivity of a measure and countable subadditivity, this
is a set of zero measure. Since $\bigcup_{i=1}^{\infty}F_i$ is a $1$-set by Theorem
4.2.13, it is a regular set.
Now if all the $F_i$ are irregular, let $\Gamma$ is a rectifiable curve then
$\mathcal{H}^1(\Gamma \cap F_i)=0$. Therefore,
\begin{equation}
\mathcal{H}^1(\Gamma \cap \bigcup_{i=1}^{\infty}F_i) =
\mathcal{H}^1(\bigcup_{i=1}^{\infty}(\Gamma \cap F_i)) \leq \sum_{i=1}^{\infty}
\mathcal{H}^1(\Gamma \cap F_i)=0
\end{equation}
Therefore, again by Theorem 4.2.13, we have that $\bigcup_{i=1}^{\infty}F_i$ is
irregular.
\end{proof}
\end{document}
答案1
为环境提供一个可选参数ex。这被称为“定理注释”：
\documentclass{article}
\usepackage{amsthm,lipsum}
\newtheorem{ex}{Exercise}
\begin{document}
See Exercise~\ref{exercise:ABC}.
\begin{ex}[Author~ABC, Chapter~X, Exercise~Y.Z]
\label{exercise:ABC}\lipsum[1]
\end{ex}
\end{document}
当您引用练习 1不过，你不会得到定理注释作为参考的一部分。不过，这似乎足够了，否则你的文本会变得混乱。