Latex的xy Pic宏包绘制hasse图之ec1中的插图

\documentclass[border=3pt]{standalone}
% \input xypic
\usepackage[all,pdf]{xy}
\newcommand{\B}{{\dir{*}}}
\begin{document}
    \begin{xy}\drop[*1]\xybox{
            (0,0)="A" *{\B}*\cir{},
            (5,8.66)="B" *{\B}*\cir{},
            (10,0)="C" *{\B}*\cir{},
            (20,0)="D" *{\B}*\cir{},
            {"A";"B":"C";"B",x} ="I" *{},
            "I";"A"**{}  **@{-},
            "I";"C"**{}  **@{-}}
        \end{xy}
\end{document}

\documentclass[border=3pt]{standalone}
% \input xypic
\usepackage[all,pdf]{xy}
\newcommand{\B}{{\dir{*}}}
\newcommand{\C}{\circ}
\def\al{\ar@{-}}
\def\xyy{\xymatrix@1}

\begin{document}
    \xyy{*=0{\B}\al[d]\al[dr]&*=0{\B}\al[d]\\*=0{\B}&*=0{\B}}
\end{document}