我正在准备一本有关Analysis的书，并且正在使用ntheorem，以便拥有自己的各种定理环境。效果很好，但是，每次我在证明或定理中开始一个枚举列表时，在定理标题和枚举列表的开头之间都会有一些额外的垂直空间。这是我的MWE：
\documentclass[a4paper,12pt,twoside]{book}
\usepackage[left=1.65cm,right=1.65cm,top=2.45cm,bottom=2.60cm]{geometry}
\usepackage{amsmath,amssymb,amscd,amsbsy,mathabx,array,color}
\usepackage{mathtools}
\usepackage{fancyhdr,framed,latexsym,multicol,pstricks,slashed,xcolor,multicol}
\usepackage{picture}
\usepackage{indentfirst}
\usepackage{enumitem}
\usepackage[amsmath,framed,thmmarks]{ntheorem}
\newtheorem{Theorem}{Theorem}
\theoremclass{Theorem}
\theoremstyle{break}
\theoreminframepreskip{0pt}
\theoreminframepostskip{0pt}
\theoremframepreskip{1cm}
\theoremframepostskip{1cm}
\theoremstyle{break}
\def\theoremframecommand{%
\psshadowbox[fillstyle=solid,fillcolor=cyan,linecolor=black]}
\newshadedtheorem{them}{Theorem}[section]
\begin{document}
\begin{them}
Let $X$ and $Y$ be sets. Then:
\begin{enumerate}
\item If $X$ and $Y$ are finite disjoint sets, then $X \bigcup$ is finite and $\overline{\overline{X \bigcup Y}} = \overline{\overline{X}} + \overline{\overline{Y}}$.
\item If $X$ and $Y$ are finite sets, then $X \bigcup Y$ is finite and $\overline{\overline{X \bigcup Y}} = \overline{\overline{X}} + \overline{\overline{Y}} \setminus (\overline{\overline{X \bigcap Y}})$.
\item If $X_1,X_2, \ldots, X_n$ are finite sets, then $\displaystyle{\bigcup_{i=1}^n X_i}$ is finite.
\end{enumerate}
\end{them}
\end{document}
任何帮助将不胜感激。