This is a system of responses to 1 of a suit openings which is used in the earliest natural Culbertson system. It has several disadvantages, particularly that invitational hands are very difficult to communicate, since 1/1 and 2/1 are the only allowed bids with between 11-12 points. This is solved by adding Limit raises and Inverted minor raises. Additionally, the strong jump shift with 17+ points (which means 30+ for the partnership -- how often does that happen?) has since been relegated to a weak bid. Artificial strong responses to a major suit have taken its place. What you see below is the original system, and is therefore out of date. See the system of SAYC or BWS for a more up-to-date treatment.