RE: [ACTION-18] use case on !ASK in FILTERS to emulate negation

Simon,

"""
Another possibility would be a binary UNSAID operator, which behave as a join with the right operator returning

    * a set with the empty binding, if the pattern does not match or
    * the empty set, if the pattern does match. 

As a result, if the pattern matches, the current result will be discarded.
"""

I don't understand this - if it's a join, and returns the empty set, won't the overall result be empty.  It's not considering the possibilities one-by-one, taking into account the variables if it's a join.  

I've taken the liberty of writing a form that makes it FILTER-like informal description which does ground the second pattern with respect to the bindings in the first part.  Do reverse the change if you meant something else and I missed the point.

	Andy