[mgoetze]

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1♣ = 11-13 bal or 17+ any
1♦ = 0-7 any

As some of you have figured out by now, I'm trying to learn the Swan 4.0 structure. Here is what it says

Quote

After 1♣ - 1♦

Weak OP may pass with diamond length, or if, lacking a 4-c M, bidding a 3-c M is unappetizing.

1♣ - 1♦; 1M

1M is NAT, NF, either weak (occasionally 3-c if OP does not want to pass 1♦) or strong (5-c or 4-c UNBAL - 4441 or longer minor).

RP may pass with 0-4 hcp. Otherwise:

1♠ 0-7 hcp, 4-c - F1 if OP is strong.
1NT 5-7 hcp, no 4-c support, usually no reasonable 5-c suit. Denies 4-c spades.
2ns 5-7 hcp, 5-c, denies 4-c spades. RP tends to prefer 1NT with 3-c support in M or with a weak 5-c suit.
2M 3-7 hcp, 4-c support. F1 if OP is strong – OP’s 3M shows MIN.
Jump in ns 5-7 hcp, good 6-c (on the 3-level, at least KQ).
2NT 5-c support, MAX. Jacoby module – OP’s 3♣ shows 11-13.

Weak OP must always pass on the next round, including over 1♠, except over 2NT.

So apparently I have a choice between pass and 1♥. If I bid 1♥ we might get to 1♠ or 2♥ on a 4-3 fit, or even 3♥ on a 5-3. We might end up in 1♥ on a 3-x fit rather than 1♦ on a 4-x fit. We could play 1NT with 18 HCP.

To my mind, all those things don't sound so bad as to outweigh the major downside of passing 1♦: the enemy have 20-27 HCP and it will be easier for them to balance themselves into the auction over 1♦ than over, say, 2♥.

So I'm inclined to bid 1♥, but I'm not sure about it. What do y'all think?

Would you agree that unfavourable is the best vulnerability for passing 1♦ and favourable is the worst?