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Arguments and values to get.



Consider
	(incf (get foo bar))
when the property does not exist.  INCF would die adding to NIL.  Thus,
to maintain simple style, you need
	(incf (get foo bar 0))
I think this is a LOT prettier than
	(setf (get foo bar)
	      (multiple-value-bind (value valid-p)
		  (get foo bar)
		(if valid-p (1+ value) 1)))
and the programmer doesn't have to worry about multiple evaluation of
FOO and BAR, since INCF is supposed to take care of that.