OK, so I’ve been looking at the 4NT opening as well. What follows is an attempted summary of what others use the bid for (or suggest it be used for):
hrothgar, on 2012-November-07, 19:09, said:
4NT Opening
An excellent eight or nine card minor
Sound playing values for the five-level (9+ playing tricks)
No more than one loser in any suit
(This certainly has merit. However I will choose to put this hand type through my 3NT bid even if it does go down).
Vampyr, on 2012-November-07, 22:32, said:
4NT specific Aces
5NT 1-loser hand, void in both majors
And if truth be told, I need to confirm with my regular partner, but we probably play 5M as the old-fashioned looking for top honours.
4NT specific Aces I found
this link. The probability of being dealt hands which meet this criteria are remote.
5NT 1-loser hand, void in both majors (Void in both majors is so rare that it doesn’t register a frequency % in BBOs deal generator, but no harm in having it as part of your agreements as I cannot think of any other use for the bid).
And if truth be told, I need to confirm with my regular partner, but we probably play 5M as the old-fashioned looking for top honours (This also makes sense as a corollary to the 4NT specific Ace ask. Now you have 11 tricks missing the top 2 honours in the suit bid asking partner if he has them. 6M = I got 1, 7M = I got both).
Zelandakh, on 2012-November-08, 05:04, said:
The 4NT opening is another one that gets discussed to death on BBF. There have also been numerous threads on this in the last year. The traditional meaning is a specific ace ask. Several top pairs use ot as some kind of extreme 2-suiter. I have not seen hrothgar's idea before but it seems to make sense as an alternative.
Cascade, on 2012-November-08, 13:38, said:
4NT both minors at least 5=6
The probability of being dealt a hand which meets this criteria is 0.29%.
deannz, on 2012-November-08, 21:38, said:
4N = good preempt (doesn;t come up often but clarifies 5m) as per Preempts from A-Z.