[pstricks] slanted text

[Zbigniew Nitecki]

In the following, I want to place the text labeling each face slanted,  
as if it were written on the face itself.
I have tried various viewpoint and viewangle values;  these appear to  
have no effect whatsoever on the text.
How can I slant the text so that it appears written on the appropriate  
face, as the two labels x+z=1 and y+z=1 are
supposed to?

\usepackage{pstricks, pst-3dplot}
\usepackage{pstricks-add}

			\begin{pspicture}(-2,-1.5)(2,2.5)
			\psset{unit=2, Alpha=25}
			\defineTColor{tGray}{gray!40}
			\pstThreeDCoor[xMin=-1.5, xMax=1.5, yMin=-1.5,yMax=1.5, zMin=0,  
zMax=1.5]
			\pstThreeDSquare[fillstyle=solid, fillcolor=gray](-1,-1,0)(2,0,0) 
(0,2,0)
			\pstThreeDTriangle[style=tGray](-1,-1,0)(1,-1,0)(0,0,1)
			\pstThreeDTriangle[style=tGray](-1,-1,0)(-1,1,0)(0,0,1)
			\pstThreeDTriangle[style=tGray](1,1,0)(1,-1,0)(0,0,1)
			\pstThreeDTriangle[style=tGray](1,1,0)(-1,1,0)(0,0,1)
			
			\pstThreeDPut(1,-1.7,-0.2){$(1,-1,0)$}
			\pstThreeDPut(1.2,1.2,0){$(1,1,0)$}
			\pstThreeDPut(-1,1.7,0.2){$(-1,1,0)$}
			\pstThreeDPut(0,0,1.2){$(0,0,1)$}
			
			\psset{viewpoint=1 3 1, viewangle=60}
			\pstThreeDPut(0.66,0,0.33){\small{x+z=1}}
			\pstThreeDPut(0,0.66,0.33){\small{y+z=1}}
			\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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