If Opener rebid a new suit:
After a 2/1 response, opener can bid a new 4+ card suit (not 3 cards) on the 2-level, so responder should raise the new suit with 4-card support. With less support, try NT, or rebid a 6+ card suit, or bid the fourth suit (artificial – called "Fourth Suit Forcing") to get more information from opener.
North:
♠ 3 2 South North
♥ A 4 1♠ 2♣
♦ A Q J 2♥ 2 NT*
♣ Q 8 6 5 4 3
* North: don’t rebid your crummy club suit. Your 2 NT rebid guarantees a diamond stopper, the only unbid suit.
If Opener raised responder’s suit:
Terrific! You have a trump suit and now should decide if it will play in game or slam.
North:
♠ A 4 South North
♥ Q 5 1♥ 2♦
♦ A K 9 8 7 3 3♦ 4 NT*
♣ K 5 4
* North: it is your decision to look for slam.
