This is another convention for investigating a slam using the bid of 4NT.
It is similar to Blackwood in asking for aces and kings but in this case the king of trumps is counted as an Ace (ie. there are now five aces).
Trumps are defined as the last suit bid.
The response to the 4NT bid, which is mandatory, is:
5C : none or 3 aces
5D : 1 or 4 aces
5H : 2 aces without the queen of trumps
5S : 2 aces with the queen of trumps
5NT can be bid to ask for the number of kings. However, the king of trumps is not included in this response because it has already been included in the response to 4NT.
The response to 5NT, which is mandatory:
5C : no kings
5D : 1 king
5H : 2 kings
5S : 3 kings
Following this response, the final contract can be bid.