\documentclass[a4paper,12pt,brazil]{article}

\usepackage[brazil]{babel}
\pagestyle{empty}
\usepackage{gastex}

\usepackage[usenames]{color}

\newcounter{conta} 
 
\begin{document}

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    \put(70,32){\makebox(0,0){$A$}}
    \put(80,32){\makebox(0,0){$B$}}
    \drawccurve[Nframe=n, fillcolor=Gray](75,28.4)(70,20)(75,11.6)(80,20)
    \drawcircle(70,20,20)
    \drawcircle(80,20,20)
    \put(75,4){\makebox(0,0){$A\cap B$}}
          \end{picture}
         }
        \end{center}

\end{document}
 \begin{center}
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    \put(25,32){\makebox(0,0){$A$}}
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    \drawcircle[fillcolor=Gray](35,20,20)
    \drawcircle(25,20,20)
    \put(30,4){\makebox(0,0){$A\cup B$}}

    \put(55,0){\framebox(40,36)}
    \put(70,32){\makebox(0,0){$A$}}
    \put(80,32){\makebox(0,0){$B$}}
    \drawccurve[Nframe=n, fillcolor=Gray](75,28.4)(70,20)(75,11.6)(80,20)
    \drawcircle(70,20,20)
    \drawcircle(80,20,20)
    \put(75,4){\makebox(0,0){$A\cap B$}}

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    \put(115,32){\makebox(0,0){$A$}}
    \put(125,32){\makebox(0,0){$B$}}
    \drawcircle[fillcolor=Gray](115,20,20)
    \drawcircle[fillcolor=White](125,20,20)
    \drawcircle(115,20,20)
    \put(120,4){\makebox(0,0){$A-B$}}

  \end{picture}
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 \end{center}
