Woodson Two-way NT
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1NT opening shows either a balanced 10-12 or a balanced 16-18. 
Responder bids 2C to ask and opener rebids:
  1) 2D, 2H or 2S with 10-12 
  2) 2NT with 16
  3) 3C with 17-18
Responder can then bid 3D to ask for a four card major.
Other responses of 2D, 2H and 2S are signoff-- even opposite a 
strong NT opening. 

If 1NT is doubled, opener redoubles to show the strong hand.