This is a plot of the execution stack (x-axis) and the operand stack (y-axis)
during the execution of the PostScript /quicksort routine. Each successive
picture is more twisted than the last. Twisting is accomplished by rotating
the coordinate system clockwise slightly around the center of each of the
dots as they are drawn. The rotation around each plotted point accumulates
to make the whole drawing curl up. The more twisted away from the original
orientation a point is, the later it occurred in time. 
In the first picture, the untwisted version, up corresponds to a deeper
operand stack (pushing things on the stack moves you up), and right
corresponds to a deeper execution stack (procedure calls and control
structures move you right). The lines follow changes in the state of
the stack between steps of the interpreter. (This was made possible by
a PostScript interpreter written in PostScript.) 

To see the twist animation, run monochrome NeWS, type "psh" to the shell,
then type "(/wherever/you/put/it/twist.ps)run".
The reason you can't just psh the file directly is that NeWS 1.1 psh
does $1 $2 $3 arg substitution, even on binary data! (X11/NeWS psh should 
work, so you can just go "psh twist.ps")

What the file twist.ps contains is a short header defining the function
"c", which reads a canvas and displayed it on the framebuffer. That is 
followed by a series of "c"'s each followed by a 1 bit deep 1152x900 
sun raster files.

	-Don Hopkins
	 (don@brillig.umd.edu)