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\begin{document}

\mingb

\title{\yuan 近\ \, 世\ \, 代\ \, 數\ \\

Modern Algebra}

\author{\fs Elbert A. Walker 艾伯特\thanks{author 作者} }

\date{6 October 1994}

\maketitle

\pskaib

\begin{abstract}

This document describes by example the use of {\tt asaetr.sty}, a \LaTeX\

style that somewhat conforms to the style used in the {\em Transactions of

the ASAE}\/. \cite{dunford} An accompanying BiBTeX style file is also used

to format the bibliography in a style similar to that used by ASAE.

\end{abstract}

\mingb

\section[導 論]{\kaib 導 論 Introduction}

群論是一門領域甚廣的學科,幾乎任何數學訓練都需要它。本章將簡單介紹一些%

古典的 非-Abelian 群論。在{\underbar{第二章}},我們將介紹同構,正規子群,

商群,直和等基本觀念。 ...

\li

群論是一門領域甚廣的學科,幾乎任何數學訓練都需要它。本章將簡單介紹一些%

古典的 非-Abelian 群論。在{\underbar{第二章}},我們將介紹同構,正規子群,

商群,直和等基本觀念。 ...

\mingb

\section{\kaib Jordan-Holder 定理}

Let $G$ be a finite group. If $G$ is not simple, then $G$ has a normal

subgroup $G_1\neq G$ such that $G/G_1$ is simple\textit{.} Just let $G_1$ be

a maximal normal subgroup in the finite group $G$\textit{.} Similarly, $G_1$

has a normal subgroup $G_2$ such that $G_1/G_2$ is simple. Thus we get a

descending chain

\[

G=G_0\supset G_1\supset G_2\supset \cdots \supset G_n=\{e\}

\]

such that $G_{i+1}$ is normal in $G_i$, and $G_i/G_{i+1}$ is simple. Now

suppose that

\[

G=H_0\supset H_1\supset H_2\supset \ldots \supset H_m=\{e\}

\]

is another such chain of subgroups. The Jordan-Holder Theorem asserts that $%

m=n$, and that there is a one-to-one correspondence between the factor

groups $G_i/G_{i+1}$ and $H_j/H_{j+1}$ such that corresponding factor groups

are isomorphic. We will prove this remarkable theorem, but first some

notation and terminology are needed. \textbf{The groups considered are not

necessarily finite.}

\begin{definition}

\ \, 設 $G$ 為一群。 $G$ 的一正規級數就是一如下之群的鍊鎖:

\[

G=G_0\supset G_1\supset G_2\supset \ldots \supset G_n=\{e\}

\]

其中,對於每一 $i$,\ $\,$ $G_{i+1}$ 皆為 $G_i$ 之正規子群。

The groups $G_i/G_{i+1}$ are the factor groups of the chain.

The length of the chain is

the number of strict inclusions in the chain. A normal series is a

composition series if each factor group $G_i/G_{i+1}$ is a simple group $%

\neq \{e\}$. Two normal series are equivalent if there is a one-to-one

correspondence between their factor groups such that corresponding factor

groups are isomorphic.

\end{definition}


\begin{theorem}[Jordan-Holder]

\ \, Any two composition series of a group are equivalent.

\end{theorem}

\proof\ \ If a group has a composition series of length

one, then the group is simple and any two composition series are certainly

equivalent. Now suppose that a group $G$ has a composition series


\begin{equation} \label{one}

G=G_0\supset G_1\supset G_2\supset \ldots \supset G_n=\{e\}

\end{equation}

of length $n>1$, and that if a group has a composition series of length less

than $n$, then any two composition series of that group are equivalent. Let

\begin{equation} \label{two}

G=H_0\supset H_1\supset H_2\supset \ldots \supset H_m=\{e\}

\end{equation}

be any composition series of $G$. Consider the series

\begin{equation} \label{three}

G=G_0\supset G_1\supset G_1\cap H_1\supset G_2\cap H_1\supset \ldots \supset

G_n\cap H_1=\{e\}

\end{equation}

and

\begin{equation} \label{four}

G=H_0\supset H_1\supset H_1\cap G_1\supset H_2\cap G_1\supset \ldots \supset

H_m\cap G_1=\{e\}

\end{equation}

Since $G_{i+1}\cap H_1$ is a normal subgroup of $G_i\cap H_1$ and $%

G_i\supset G_{i+1}$, the Third Isomorphism Theorem (\textbf{2.3.12}) yields

\[

(G_i\cap H_1)/(G_{i+1}\cap H_1)=(G_i\cap H_1)/(G_{i+1}\cap (G_i\cap

H_1))\approx

\]

\[

G_{i+1}(G_i\cap H_1)/G_{i+1},

\]

and $G_{i+1}(G_i\cap H_1)$ is a normal subgroup of $G_i$ since it is a

product of two normal subgroups. Since $G_i/G_{i+1}$ is a simple group, $%

(G_{i+1}(G_i\cap H_1))/G_{i+1}$ is either $G_i/G_{i+1}$ or $G_{i+1}/G_{i+1}$%

. That is, $G_{i+1}(G_i\cap H_1)$ is either $G_{i+1}$ or $G_i$. Therefore,

if we remove repetitions from

\[

G_1\supset (G_1\cap H_1)\supset (G_2\cap H_1)\supset \ldots \supset (G_n\cap

H_1)=\{e\},

\]

we get a composition series for $G_1$. By our induction hypothesis, the

resulting composition series is equivalent to the composition series

\[

G_1\supset G_2\supset \ldots \supset G_n=\{e\}\text{,}

\]

and hence (\ref{one}) and (\ref{three}) (with repetitions removed) are

equivalent. $\cdots$



\section{\kaib 問 題 集 Problem set}

\begin{enumerate}

\item 試証: 若 $G$ 有一合成級數,則任何正規子群 $G$ 都有合成級數。

\item 試証: 若 $N$ 在 $G$ 中為正規,且若 $G$ 有一合成級數,則 $G/N$ 亦然。

\item Suppose that $G$ has a composition series and that $N$ is normal in $%

G $. Prove that $G$ has a composition series of which $N$ is a member.

\item Suppose that $G$ has a composition series. Prove that any normal

series of $G$ has a refinement that is a composition series.

\item \label{zasslemma}(\textbf{Zassenhaus's Lemma}) Let \textit{A} and $B$

be subgroups of a group $G$, and let $M$ and $N$ be normal in \textit{A} and

$B$, respectively. Prove that

\end{enumerate}

\section{圖形與表格}

\begin{figure}[htb]

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\caption[原始之圖]{原始之圖 Primitive figure.}

\end{figure}

{

\renewcommand{\footnoterule}{}

\begin{table}[hbp]

\footnotesize

\vglue0pt

\caption{出版工具 Comparison of Publishing Tools}

\begin{center}

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\begin{center}

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\begin{tabular}{crr} \thickhline

Tool & \multicolumn{1}{c}{Learning Curve %\footnote{1.0 being easiest}

}& \multicolumn{1}{c}{Support %\footnote{10.0 being the best}

}\\ \thinhline

FrameMaker & 5.0 & 6.0 \\

Troff & 10.0 & 1.0 \\

\TeX %\footnote{\TeX\ is the winner!}\/

& 7.0 & 10.0 \\ \thickhline

\end{tabular}

\linethickness{0pt}

\end{center}

\end{center}

\end{table}

}



\begin{thebibliography}{9}

\bibitem[杜甫 1964]{dunford} N. Dunford and J. Schwartz, 泛函分析,

\bibitem{} M. Struwe, \emph{Semilinear wave equations}, Bull. Amer. Math.

Soc. \textbf{26} (1992), 53-85.

\bibitem{} W.P. Thurston, \emph{Geometry and topology of three manifolds},

Lecture notes, Princeton Univ., NJ, 1979.

\end{thebibliography}

\end{document}


\begin{theindex}

\item 代數 1, 12

\item series 2, 33

\subitem convergent, 22, 55

\indexspace

\end{theindex}


\end{document}