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Question

这是我第一次使用 latex 绘制图表。我已将tkz库和 tkz 库包括在内shapes.multipart。在处理我的代码时，我得到了一堆令人讨厌的错误，除此之外还有

!Package pdg Error: Arrow end type ``stealth''' unknown. See the pgf package documentation for explanation.

有人告诉我，我需要在文档中包含 shapes.multipart 包才能消除此错误，但显然它不起作用。有人能帮我解决这个问题吗？

\documentclass[11pt,a4paper,oneside]{article}
\usepackage[italian]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsfonts}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{centernot}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{shapes.multipart}

%opening
\title{Esame di Algebra}
\author{haunted85}

\begin{document}

\maketitle
\newpage

... blah blah... paper content

\subsection{} L'insieme proposto non risulta totalmente ordinato in quanto $15$ e $21$ non sono tra loro confrontabili, in particolare $15 \centernot\sigma 21$ e $21 \centernot\sigma 15$. 
\begin{tikzpicture}[->,>=stealth',shorten >=1pt,auto,node distance=2.8cm,semithick]
    \tikzstyle{every state}=[fill=blue,draw=none,text=black]

    \node[initial,state] (A)                    {$49$};
    \node[state]         (B) [below of=A]       {$35$};
    \node[state]         (C) [below left of=B]  {$15$};
    \node[state]         (D) [below right of=B] {$21$};
    \node[state]         (E) [below of=B]       {$4$};
\path   (A) edge    node{} (B)
        (B) edge    node{} (C)
        (B) edge    node{} (D)
        (C) edge    node{} (E)
        (D) edge    node{} (E);
\end{tikzpicture}
\end{document}