标题表明了问题所在。我正在准备一个幻灯片来展示我的项目，但编译后我发现所有的 0 都消失了。任何解决方案都将不胜感激。
我的代码是：
\documentclass[teal]{beamer}
\setbeamertemplate{navigation symbols}{}
%\usepackage{beamerthemeshadow}
\usepackage{color}
\usepackage{amssymb}
\usepackage{amsmath,amssymb,amsthm}
\usepackage{amsfonts}
\usepackage{mathptmx}
\usepackage{amssymb}
\usepackage[mathscr]{euscript}
\usepackage{mathrsfs}
\usepackage{amsthm}\input{amssym.def}
%\usetheme{Montpellier}%
\usetheme{PaloAlto}
\setbeamercolor{frametitle}{fg=black,bg=cyan!60}
%\setbeamercolor{title}{fg=blue,bg=yellow}
\beamertemplateshadingbackground{cyan!25}{teal!50}
\definecolor{exam}{rgb}{0.0,0.30,0.0}
\definecolor{rem}{rgb}{0.50,0.00,0.50}
\definecolor{thm}{rgb}{0.40,0.00,0.00}
\definecolor{primary}{rgb}{0.60,0.70,0.89}
\newcommand{\lcb}{\overline{\mathcal{L}}}
\newcommand{\rb}{\overline{\mathcal{R}}}
\newcommand{\hb}{\overline{\mathcal{H}}}
\newcommand{\jcb}{\overline{\mathcal{J}}}
\newcommand{\db}{\overline{\mathcal{D}}}
\newcommand{\lc}{\mathcal{L}}
\newcommand{\rc}{\mathcal{R}}
\newcommand{\hc}{\mathcal{H}}
\newcommand{\jc}{\mathcal{J}}
\newcommand{\dc}{\mathcal{D}}
\newcommand{\ec}{\mathcal{\eta}}
\newcommand{\lp}{\mathcal{L}^+}
\newcommand{\rp}{\mathcal{R}^+}
\newcommand{\hp}{\mathcal{H}^+}
\newcommand{\dpp}{\mathcal{D}^+}
\newcommand{\jp}{\mathcal{J}^+}
\newcommand{\ld}{\mathcal{L}^{\bullet}}
\newcommand{\rd}{\mathcal{R}^{\bullet}}
\newcommand{\hd}{\mathcal{H}^{\bullet}}
\newcommand{\dd}{\mathcal{D}^{\bullet}}
\newcommand{\jd}{\mathcal{J}^{\bullet}}
\newcommand{\red}{\mathbf{R}e^{\bullet}}
\newcommand{\lzd}{\mathbf{LZ}^{\bullet}}
\newcommand{\rzd}{\mathbf{RZ}^{\bullet}}
\newcommand{\lzp}{\mathbf{LZ}^{+}}
\newcommand{\rzp}{\mathbf{RZ}^{+}}
\newcommand{\slp}{\mathbf{SL}^{+}}
\newcommand{\vb}{\mathbf{B}}
\newcommand{\vd}{\mathbf{D}}
\newcommand{\vi}{\mathbf{I}}
\newcommand{\vn}{\mathbf{N}}
\newcommand{\vln}{\mathbf{LN}}
\newcommand{\vrn}{\mathbf{RN}}
\newcommand{\vlp}{\mathbf{L}^{+}}
\newcommand{\vrp}{\mathbf{R}^{+}}
\newcommand{\bi}{\mathbf{BI}}
\newcommand{\lbi}{\mathbf{LBI}}
\newcommand{\rbi}{\mathbf{RBI}}
\beamersetuncovermixins{\opaqueness<1>{25}}{\opaqueness<2->{15}}
\begin{document}
\title{A study}
\author{Hiren Garai}
\date{}
\begin{frame}
\begin{block}{\begin{center} \huge \textbf{A study}
\end{center}}
\end{block}
\begin{center}
\textcolor{blue}{Hiren Garai} \\
\textcolor{black}{\small{Department of Mathematics
}}
\end{center}
\end{frame}
\section{Introduction}
\begin{frame} \frametitle{Introduction}
\beamertemplateshadingbackground{white}{white}
%\beamertemplateshadingbackground{blue!25}{blue!50}
Functional Analysis is mainly concerned with the structure of infinite dimensional vector spaces and transformations, which are frequently called operators between such spaces.
In the sixities, 2-metric spaces were introduced by G\"ahler \cite{Ga 1}, \cite{Ga 2}.
\begin{Definition} Let $X$ be a nonempty set, and let $R$ be the set of all reals and ${R^+}$ be the set of positive reals. A function $d : X \times X \times X \implies {R^+} \cup \{{0}\}$ satisfying:
\begin{itemize}
\item[(D1)] \; For distinct points $x, y,\in X$, there is $z \in X$, such that $d(x,y,z) \neq 0.$
\item[(D2)] \; $d(x,y,z) = 0 $ if two of the triple $x,y,z \in X$ are equal.
\item[(D3)] \; $d(x,y,z) = d(x,z,y) = \cdots $ (symmetry in all three variables).
\item[(D4)] \; $d(x,y,z) \leq d(x,y,a) + d(x,a,z) + d(a,y,z), \, \forall x,y,z,a \in X. $
\end{itemize}
is called a $2$-metric, on $X.$ The set $X$ equipped with such a 2-metric is called a \textit{$2$-metric space.}
\end{Definition}
\end{Document}
谢谢。
答案1
删除\input{amssym.def}即可取回 0。
其他一些评论：
你不需要
\usepackage{color}使用 beamer\end{frame}不见了\end{document}不应该\end{Document}使用
\authoretc 将\begin{document}其包含在 pdf 元数据中
\documentclass{beamer}
%\input{amssym.def}
\begin{document}
\begin{frame}
$\{ 0 \}$
\end{frame}
\end{document}