You could have an agreement that a double of an alerted 1
♦ always shows diamonds, then there would be no problem here. I've never heard of anyone actually having that agreement.
My understanding is that this pair plays that a double of an artificial 1
♦ shows diamonds, whereas a double of a natural 1
♦, even if alerted, is for take out. That agreement is very common.
This sort of conditional agreement is unplayable (in the absence of UI) unless you find out whether 1
♦ is natural or artificial before you double, whether at the beginning of the round or in response to an alert.
If you always find out at the beginning of the round, your partner will act on the basis that you know the meaning of their 1
♦.
If you always ask (or consult their convention card), your partner will act on the basis that you know the meaning of their 1
♦.
The knowledge that you've done neither of these things is UI to partner. Therefore he must always act on the basis that you know the meaning of their 1
♦.
lamford, on 2015-June-02, 09:53, said:
The lack of a question is not UI, unless one sometimes asks and sometimes doesn't; we are not told that is the case. And if 1D was alerted because, as someone suggested, they were playing Walsh, then it would be ludicrous to bid 2♦ on this hand, knowing that diamonds are 4-1 or even 5-0. It could have been, from North's point of view, that South thought they were playing T-Walsh, and did not ask, but then finds they are playing Walsh. Not asking because you think you know is certainly not an infraction, whether it transpires you were right or not.
It follows that if opponents are playing Walsh, North must act on the basis that South knew that 1
♦ was natural. And if 1
♦ was artificial, as it was, North must act on the basis that South knew that likewise.