Weak NT
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After X
- pass of immediate natural 2m is forcing
- double of 2m is penalties
- pass of immediate natural 2M is non-forcing
- double of 2M is takeout
- first-chance bids are analogous to, 1NT (2M) ??. That is TRFs from 2NT ['transfer-influenced']
- doubling an artificial escape that we do not expect them to play (ex. TRF) shows values
- doubling an either-or escape is as 2m/2M split above (ex. 2D = D+H, X = penalties of diams)

If advancer establishes values then subsequent doubles are penalty

A double of an artificial 2C/D/H/S/NT shows a good hand (15+)
- pass is non-forcing
- double is takeout
- first-chance bids are transfer-influenced as above

3-level bids are intermediate

Strong NT
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After X
- pass is non-forcing
- double is takeout
- after 3rd hand's pass (or strong XX) 2C is a scramble
- first-chance bids are transfer-influenced

A double of an artificial 2C/D/H/S shows the suit named

3-level bids are disruptive

Over weak or strong
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2C is Landy, 5-4 major either longer
- 2D for longer major {then 2S = mild try, 3m = Nat INV}
- after X; Pass/2D natural, XX for longer major

2NT is 2-suited {responses?}

Passed Hand
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- X is 4S and 5-other suit
- 2C still both majors is 5S/4H or 5/5