How would you interpret the double here: 1D-(P)-1N-(X)? I have had two EXPERTS tell me that it means "p, please bid", but I cannot find a written reference for this. I have had others say that any X of NT is for penalty, but my research confirms this only for a NT opening, not response. Seagram's "25 Ways to Compete in Bidding" says that a requirement for a TO double is "the opponent's last bid was a suit, not notrump". Would your answer change for based on vulnerability?