\setlength\itemsep 抛出一个奇怪的错误

Question

我必须编辑一个 LaTeX 模板以完成一项作业，该作业涉及解决多项选择题。其中一个问题的代码如下：

\begin{list}{$\square$}{}
\setlength\itemsep{-1.5em}
\item The current observation $x_t$ is conditionally independent of all 
 other observations given the current state $y_t$\\
\item The current observation $x_t$ is conditionally independent of all 
other states given the current state $y_t$\\
\item The current state $y_t$ is conditionally independent of all states given the previous state $y_{t-1}$\\
\item The current observation $x_t$ is conditionally independent of $x_{t-2}$ given the previous observation $x_{t-1}$.\\
\item None of the above
\end{list}

问题是我不知道如何标记我的答案（这些选项中只有两个是正确的，应该用黑色方块标记）。我尝试{$\square$}从第一行中删除，并$\square$在每个项目旁边添加，在$\blacksquare$我想要标记的选项旁边添加。

\begin{list}{}
\setlength\itemsep{-1.5em}
\item $\square$ The current observation $x_t$ is conditionally independent 
 of all other observations given the current state $y_t$\\
\item $\square$ The current observation $x_t$ is conditionally independent 
 of all other states given the current state $y_t$\\
\item $\square$ The current state $y_t$ is conditionally independent of all 
 states given the previous state $y_{t-1}$\\
\item $\square$ The current observation $x_t$ is conditionally independent 
 of $x_{t-2}$ given the previous observation $x_{t-1}$.\\
\item $\square$ None of the above
\end{list}

这对于上一个问题有效。但是对于这个问题，当我执行并编译时，发生了这种情况。

就是那个讨厌的 !-1.5em。我不知道如何去掉它。我尝试删除，\setlength\itemsep{-1.5em}但这会导致项目之间的间距增加到默认值，并且此页面的内容会溢出到下一页，这对于自动评分器来说是不可接受的。我该怎么办？这非常烦人。

这是我在该行遇到的错误\setlength\itemsep{-1.5em}。 (正如答案所说，我也尝试过将其放在\itemsep花括号中，但无济于事。)

Answer 1

环境list需要两个参数，而在第二个示例中，您只输入了一个参数。因此，它使用下一个标记（即）\setlength作为其第二个参数。因此，使用\begin{list}{}{}而不是\begin{list}{}可以消除错误。

至于您最初试图解决的问题：\item宏有一个可选参数，您可以使用它来指定其标签。因此，下面的代码应该可以满足您的要求。

\documentclass{article}

\usepackage{amssymb} %% <- for \square and \blacksquare

\begin{document}

\begin{list}{$\square$}{}
\setlength\itemsep{-.4em}
\item The current observation $x_t$ is conditionally independent of all 
 other observations given the current state $y_t$
\item[$\blacksquare$] The current observation $x_t$ is conditionally independent of all 
other states given the current state $y_t$
\item[$\blacksquare$] The current state $y_t$ is conditionally independent of all states given the previous state $y_{t-1}$
\item The current observation $x_t$ is conditionally independent of $x_{t-2}$ given the previous observation $x_{t-1}$.
\item None of the above
\end{list}

\end{document}

你可以通过定义来节省一些输入

\newcommand*\correctitem{\item[$\blacksquare$]}

并使用它而不是每次都输入它。

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顺便说一句，第二个参数的内容list是在实际列表开始之前执行的。将其放在\setlength\itemsep{-.4em}这个参数中会更合适，如下所示：

\begin{list}{$\square$}{\setlength\itemsep{-.4em}}

因为\itemsep这没什么区别，但是如果你想设置例如\topsep，在环境内这样做实际上已经太晚了。

Answer 2

您不需要疯狂地设置，只需使用带有选项的包\itemsep即可。enumitemnosep

\documentclass{article}
\usepackage{amssymb} 
\usepackage{enumitem}
\renewcommand{\labelitemi}{$\square$}
\begin{document}
\begin{itemize}[nosep]
\item The current observation $x_t$ is conditionally independent of all 
 other observations given the current state $y_t$
\item[$\blacksquare$] The current observation $x_t$ is conditionally independent of all 
other states given the current state $y_t$
\item[$\blacksquare$] The current state $y_t$ is conditionally independent of all states given the previous state $y_{t-1}$
\item The current observation $x_t$ is conditionally independent of $x_{t-2}$ given the previous observation $x_{t-1}$.
\item None of the above
\end{itemize}
\end{document}