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\usepackage[francais]{babel}
\usepackage{mafr}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{lmodern}
\usepackage[dvipsnames]{xcolor}
\usepackage{pstricks}
\usepackage{pst-node}
\begin{document}
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\pcline(0,0)(2,0)\nbput[labelsep=10pt]{$a$}%
\pcline(2,0)(2,1)\nbput*[nrot=90]{$b$}%
\pcline(0,0)(2,1)\naput*[nrot=:U]{$c$}%
\end{pspicture}
\end{document}
