********** Note to 151 videotape class students on anomalies of the clipper function*********
The clipper algorithm seems to behave strangely in the case when the polygon
to be clipped has a side or corner in common with a side or corner of the
window. What happens in this case is that the corner point of the window
is repeated in the output polygon.
E.G. If (10,20) is both a point on the polygon, and a corner of the window
the output file might have:
....
....
....
10,20
10,20
....
....
....
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