答案1
您应该收到有关未定义控制序列的错误:
<recently read> \mathrlap
l.8 \end{tikzcd}
The control sequence at the end of the top line
of your error message was never \def'ed.
缺少mathtools
提供的包。\mathrlap
因为\LARGE
它也不是一个接受参数的宏,而只是切换字体大小,所以我相应地调整了它的定义\pb
。
代码
\documentclass{article}
\usepackage{amssymb} % for \lrcorner
\usepackage{mathtools} % for \mathrlap
\usepackage{tikz-cd}
\newcommand*{\pb}{\mbox{\LARGE$\mathrlap{\cdot}\lrcorner$}}
\begin{document}
\begin{tikzcd}
A \arrow[dr, phantom, "\pb", very near start] \\
& B
\end{tikzcd}
\end{document}