This chapter is our defense when an opponent opens a Multi 2♦, which is a weak two in an unknown major (and sometimes a strong option). We are allowed written notes for this at the table. The overall framework is the "Option 2" style: our direct suit bids are natural, our double is a split-range balanced or strong hand, and 2NT is natural. This is a complex defense; the skeleton below captures the main agreements and leaves the deep sub-auctions to be filled in later.
Three ideas carry most of the defense. First, a direct double is a split-range hand: 13-15 balanced, 19+ balanced, or 18+ unbalanced. Second, direct suit bids are natural, and 2NT is a natural 16-18. Third, after we double, responder answers roughly as if we had opened a strong notrump, so 3♣ is Stayman and 3♦/3♥ are transfers.
Because we may not yet know which major the opener holds, the notes spend a lot of care on how to show stoppers in an unknown suit and how to cuebid when no suit is known. Those refinements are noted but kept shallow here.
Our calls in direct seat over the 2♦ opening.
Dbl 13-15 or 19+ balanced, or 18+ unbalanced (13-16 if partner is a passed hand). 2♥ / 2♠ Natural. The cheapest bid in a major is natural, not a cuebid. 2NT Natural, 16-18. Systems on as for a 2NT opener. 3♣ / 3♦ Natural. 3♦ over 3♣ is artificial, like a cuebid. 3♥ / 3♠ Strong. The other major is a cuebid. 3NT Based on a long minor. 4♣ asks. 4♣ Leaping Michaels: clubs and a major, GF. 4♦ asks. 4♦ Leaping Michaels: diamonds and a major, GF. 4♥ is pass-or-correct.
After 2♦-Dbl-Pass, responder bids as though partner opened a strong notrump. The double's three ranges (13-15 balanced, 19+ balanced, 18+ unbalanced) get sorted out on the next round.
Pass Willing to defend 2♦ doubled. Need not be a big diamond hand. 2♥ / 2♠ Natural, competitive. 2NT 5+ ♣, requests 3♣ when the double is 13-15. 3♦ / 3♥ Transfer, invitational or better. 3NT 11-16 with a ♦ stopper. 4♣ / 4♦ Strong invitation in the minor. 4♥ / 4♠ Natural, non-forcing. 4NT Straight Blackwood.
Often our first chance to act comes after 2♦-Pass-2M, where responder's 2♥ or 2♠ is pass-or-correct. Advancer treats this much like a direct overcall of a known weak two.
Dbl Takeout of ♥, or any 18+. Lebensohl applies. May be light with short ♥. 2♠ Natural, limited by the failure to double. 2NT 14-18, respond as to a 2NT opener. 3♣ / 3♦ Natural, as a direct minor overcall. 3♥ / 3♠ Natural. The other major is a cuebid. 3NT Natural, 22-24 or a long running suit. 4♣ / 4♦ Leaping Michaels: 5+ in the minor and 5+ in the unknown major, GF.
In the balancing seat, after the auction has died in a major, our actions are the same shape but weaker than the direct versions.
Dbl Takeout. Lebensohl applies. 2NT Both minors, moderate values. Other Natural, weaker than a direct call would be.
Two more situations round out the defense. Over a preemptive raise (2♦-Pass-3M or a jump to game), double is takeout or any 18+, and passing then doubling is takeout. Over a natural 2NT asking bid by responder (2♦-Pass-2NT), double shows 15+, suit bids are natural, and 3NT shows tricks. If the Multi is passed out to us (2♦-Pass-Pass), we bid as over a weak 2♦.