Used over opponents notrump openng.
Double = Unspecified one-suiter, relays responder to 2C
2C = Clubs and another suit
2D = Diamonds and a major
2H = Hearts and Spades
2NT = Major-minor two-suiter, very strong hand hand (6-5 or better)
(This relays partner to 3C, over which opener identifies
his two suits via a fairly complicated code.)
3NT = Two-suited in the majors, very strong hand
2S = Spade one-suiter, 6-card suit or strong 5-carder
3-bids = Long suit (7+ cards), preemptive
AFTER THE DOUBLE:
Responder bids 2C to let the doubler show his suit. The doubler can
pass if the suit was clubs; otherwise the doubler bids the suit. If the doubler holds a
strong hand with game interest, he can jump to 3 of the suit. Responder is not forced to take the 2C relay if he has his own suit (a
6-card suit or good 5-carder). After the overcaller shows his suit, 2NT by responder shows a good
game invitation. A raise shows a fit, but not enough for a "serious"
AFTER THE 2C, 2D OR 2H OVERCALL:
Responder can pass or ask for overcaller's second suit by
bidding the cheapest suit (2D over a 2C overcall, etc.).
If responder "skips" the cheapest suit to bid another suit (i.e., 2H
over a 2C overcall), responder is showing his/her own 6-card suit or strong 5-carder.
2NT by responder is a strong game invitation and asks opener to
bid the other suit at the 3-level. If responder asks for the second suit
and then bids 2NT, it's a strong game invitation in the second suit.
Raises of minors tend to be preemptive. Raises of majors are mildly
invitational, since 2NT is available to show a good invitational hand.
OVER OPPONENTS' INTERFERENCE
If the opponent bids or doubles directly after the DONT overcall, responder may continue to inquire
into the bidder's suit(s)
The general meanings of responder's bids are:
Pass = play in the current contract
Redouble (over a double) = asks overcaller to bid the second suit
Double (of a natural bid) = asks overcaller to bid the second suit
This double shows some high cards and tolerance for all unbid suits.
Double (of an artificial bid) = lead directing
[ some partnerships have the double over the artificial bid mean the same thing as the double over opponents' natural bids]
Any suit bid = responder is showing his/her own long suit