答案1
我将这个和我之前的回答放在社区维基上,以允许其他人在认为不适合回答此类问题时进行更改或删除。
\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{fit,bending}
\begin{document}
\begin{tikzpicture}[bullet/.style={circle,fill,inner sep=1pt}]
\begin{scope}[local bounding box=stuff]
\path foreach \Y in {1,2,3,4}
{(225-\Y*90:1) node[bullet,label=above:$P_\Y$] (B\Y){}};
\draw[thick,-stealth,shorten >=2pt,shorten <=2pt]
(B1) edge[bend left] (B2) (B2) edge[bend left] (B1);
\end{scope}
\node[circle,draw,fit=(stuff)]{};
\end{tikzpicture}
\end{document}