Ralph and others:
I do not see a real problem. It is quite easy to differentiate between unary
and binary "not". It is not needed to make "not" a problem.
A not B -> the only sensible implementation is A and not B
A adj not B -> not is clearly unary
A and not B -> the less lazy way to say A not B
not B -> user is testing our system
Without causing any problems for the standard both the "and" and "and not"
forms can be allowed (if only to avoid discussions about "not" and "and
not", the retrieval community seems split in the middle about this)