quote:

can you give me an example why "((ab)c)d" is also a combination?
I think it's the same as "(ab)cd"
I guess you're right... I was just laying down all the choices, so I could later "trim"/simplify them.

It looks as if the outer parentheses will only make sense if the operator before 'c' is a low precedence one (+ or -); if that is the case, then the inner parentheses will not be needed and so becomes '(abc)d'... On the other hand, if it's a high precedence one (* or /) then the outer parentheses will not be needed and it becomes '(ab)cd'...

Maybe those 7 cases someone else pointed out as being used by the java applet will be enough... Haven't checked into it yet though...
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Later,   [b]Mad[/b]ruga