答案1
以下是一种方法:
\documentclass{article}
\usepackage{amssymb}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}[row sep=1.5cm, column sep=1.7cm]
& A \\
\{a, b\}\urar & \{a, c\}\uar \arrow[from=dr]& \{b, c\}\ular \\
\{a \}\uar\urar & \{b\}\ular[crossing over] \urar[crossing over] & \{ c\} \uar\\
& \varnothing\ular\uar \urar
\end{tikzcd} %
\end{document}