- X - 4 or more spades
- 1S - 3 or fewer spades, requests partner bid 1NT with 12-13 balanced
The idea behind this (as far as I can tell) is that with a balanced hand with 10-11 points and at most 3 spades it is risky to jump to 2NT (or 2Ha) opposite 12-13, since the heart suit is a likely source of tricks for the opponents. However, we have encounted some problems bidding hands with 6+ spades with this approach. Does anybody have a reference explaining this modified double in more detail, along with subsequent bids?