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[Ken Walter <kgw0net@stiscan.com>]

 In addition to ? + and *, a useful notation could be "list"
 of the form something like:
 	E = S / T;
 which would mean
 	E = T

 	   | E S T;

 This would produce two lists of Ss and Ts.
 This would automatically take care of what I think is one of the most
 frequent transforms of the parse tree.
 Processing the list from one end or the other would take care of
 associativity.