gistfile1.tex

\documentclass{standalone}

\usepackage{standalone}
\usepackage{tikz}

\newcommand { \U } { (-2, -2) rectangle ( 3,  2) (-2,  2) }
\newcommand { \A } { ( 0,  0) circle    ( 1)     ( 0,  1) }
\newcommand { \B } { ( 1,  0) circle    ( 1)     ( 1,  1) }

\newcommand { \venn } {
  \draw \U node [text = black, below right] { $U$ }
        \A node [text = black, above]       { $A$ }
        \B node [text = black, above]       { $B$ } ;
}

\newcommand { \union }[2] {
  \scope
    \fill[red] { #1 } ;
    \fill[red] { #2 } ;
  \endscope
}

\newcommand { \intersection }[2] {
  \scope
    \clip      { #1 } ;
    \fill[red] { #2 } ;
  \endscope
}

\newcommand { \difference }[2] {
  \scope[even odd rule]
    \clip      { #2 } (-1, -1) rectangle ( 1,  1) ;
    \fill[red] { #1 }                             ;
  \endscope
}

\begin{document}
  \begin{tikzpicture}
    \difference{ \A } { \B }

    \venn
  \end{tikzpicture}
\end{document}