XGID=-A-AbBCBBB-------b-dbBbab-:0:0:1:54:6:6:0:7:10
Match Play. Double Match Point. How should Red play 54?
In such positions the five-point prime must be kept. Therefore 21/16 is mandatory. The spare on the 6-pt must also be kept for attacking purposes.
Ergo, the only logical move is 21/12.