Did some checking: my verification for the example nested parentheses seems to hold true for all the other nested parentheses! So, it looks as if they are not needed as any expression using them can be rewriten using only one set instead of two... In that case, we get left with only 7 diferent cases... [Smile] Does that 7 ring a bell on anyone? [Smile]
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Later,   [b]Mad[/b]ruga