错误信息不明确的问题

Question

\begin{align*}
P(A) \cap P(B) & = \lbrace x \mid x \in P(A) \and x \in P(B) \rbrace \\
               & = \lbrace x \mid x \subseteq A \and x \subseteq B \rbrace \\
               & = \lbrace x \mid x \subset (A \cap B) \rbrace \\
               & = \lbrace x \mid x \in P(A \cap B) \rbrace \\
               & = P(A \cap B) 
\end{align*}

第一行错误：Missing \endgroup inserted

我应该怎么办？

Answer 1

您可能需要一个“逻辑与”，即\land而非\and。

\documentclass{article}

\usepackage{amsmath}

\begin{document}
\begin{align*}
P(A) \cap P(B) & = \lbrace x \mid x \in P(A) \land x \in P(B) \rbrace \\
               & = \lbrace x \mid x \subseteq A \land x \subseteq B \rbrace \\
               & = \lbrace x \mid x \subset (A \cap B) \rbrace \\
               & = \lbrace x \mid x \in P(A \cap B) \rbrace \\
               & = P(A \cap B) 
\end{align*}
\end{document}