Developed by William Cole. You can apply when you get 1 Major response to your 1 Minor openning. Bidding 2 Clubs invites the responder to interpret his hand. 2 Diamonds response of the responder indicates a weak hand or 4 cards major. Repeat of the major promises a good hand and 5 cards major. Bidding the other major is natural and shows 5-4 major distribution.
After the 2 Diamonds response of the responder, Opener's support of the major in 2nd level shows 3 cards of that major. Responder passes with 5 cards but bid 2 NT with 4 cards and sufficient point. Otherwise he could again pass with a poor hand and 4 cards of major.