-\renewcommand{\vec}[1]{{\bf #1{}}}
-
-
-\newtheorem{theorem}{Theorem}[section]
-\newtheorem{lemma}[theorem]{Lemma}
-\newtheorem{proposition}[theorem]{Proposition}
-\newtheorem{corollary}[theorem]{Corollary}
-
-\newenvironment{proof}[1][Proof]{\begin{trivlist}
-\item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}}
-\newenvironment{definition}[1][Definition]{\begin{trivlist}
-\item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}}
-\newenvironment{example}[1][Example]{\begin{trivlist}
-\item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}}
-\newenvironment{remark}[1][Remark]{\begin{trivlist}
-\item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}}
-
-\newcommand{\qed}{\nobreak \ifvmode \relax \else
-\ifdim\lastskip<1.5em \hskip-\lastskip
-\hskip1.5em plus0em minus0.5em \fi \nobreak
-\vrule height0.75em width0.5em depth0.25em\fi}
+\renewcommand{\vec}[1]{{\bm #1{}}}
+
+%
+% theorem environment
+%
+% common
+\theoremstyle{plain}
+\theoremseparator{:}
+\theorembodyfont{\normalfont}
+\theoremsymbol{}
+% theorem
+\shadecolor{ctheorem}
+\newshadedtheorem{theorem}{Theorem}[section]
+% definition
+\shadecolor{cdefinition}
+\newshadedtheorem{definition}[theorem]{Definition}
+% remark
+\shadecolor{cremark}
+\newshadedtheorem{remark}[theorem]{Remark}
+% proof
+\theoremstyle{nonumberplain}
+\theoremsymbol{\rule{1ex}{1ex}}
+\shadecolor{cproof}
+\newtheorem{proof}{Proof}