I am the author of the book BFUN: Bridge For the UNbalanced. In the Author's Note section, I discuss the issue of responses in 3-card majors. I cite a Usenet posting from Kurt Schneider, dated sometime in 2006, in which he cites an official response from Official ACBL Tournament Directors Mike Flader and Rick Beyes: "Here is the official answer. This response in a three card major is a treatment, not a convention. As such, it is legal with the appropriate alerts and explanations in all ACBL-sanctioned play." I have confirmed with Kurt that this is accurately reported correspondence between him and the ACBL. In my BFUN system, the 1♦-1M and 1♥-1♠ sequences are very frequent. They are natural (but alertable as 3+) in that BFUN is a canape system in which a 5+-card primary major suit often accompanies an opening of a 4+-card secondary suit. The response is natural in the sense that it relates to the suit bid and suggests it as a trump suit. Unless the ACBL has retracted this stand since 2006 (which I doubt), I don't think there is any ACBL constraint against use of this treatment. BTW, I have heard that the upcoming version of the ACBL Convention Charts will indicate that treatments and conventions are to be allowed unless specificially disallowed. I believe this will help with resolving some of this type of ambiguity or lack of clarity.
