[pstricks] multido again

[Zbigniew Nitecki]

I am trying to draw a series of arcs joining the same endpoints, with  
successively larger radii of curvature.  The following code returns an  
error indicating that an exclamation point somewhere is being read as  
a missing number (treated as zero).  What am I doing wrong? (It seems  
not to matter whether or not I put an exclamation point before the  
lone \rt in the first angle specification for the arc).

	\begin{pspicture}(-3,-3)(3,3)
		\psarc[linewidth=1.2pt,arrows=->](0,0){2}{0}{180}
		\multido{\rt=10+10}{4}{%
			\psarc(!0 \rt\space 2 mul cos neg)%
				{!\rt\space cos 2 mul}{\rt}{!180 \rt\space sub}
		}
	\end{pspicture}



Zbigniew Nitecki
Department of Mathematics
Tufts University
Medford, MA 02155

telephones:
Office    (617)627-3843
Dept.    (617)627-3234
Dept. fax    (617)627-3966
http://www.tufts.edu/~znitecki/

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