Lightner DBL

DBL of 3NT uncontested, asks for a lead in Dummy's first suit.

DBL of 3NT after we bid, forbids the lead in our suit.

DBL of a slam alerts partner of our void. If it is not likely that we have one it requires a lead in Dummy's first suit.

DBL after 1NT – 3NT or 1NT – invitation – 3NT shows at least KQJ10x in unknown suit.