\documentclass[pstricks,border=15pt]{standalone}

\begin{document}
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	\psarcn[linecolor=blue](2.5,2.5){2}{0}{0}
	\psellipticarc[linecolor=green](2.5,2.5)(1,2){0}{0}
	\psellipticarcn[linecolor=magenta](2.5,2.5)(2,1){0}{0}
\end{pspicture}

\begin{pspicture}[showgrid=true,arrowinset=0,arrows=->](5,5)
	\psline(1,1)(1,1)
	\psarc[linecolor=red](2.5,2.5){1}{0}{!0}
	\psarcn[linecolor=blue](2.5,2.5){2}{0}{!0}