Baron System
An English System developed in the 1940s by Leo Baron.
An equivalent of a weak take-out double. It is usually made with a singleton or void in the opponents suit, and the most likely distribution is 4-4-4-1. The maximum strength is 13 points, and the minimum depends on vulnerability.
An invitation to a slam contract if partner has good trumps. A bid of the suit next below the agreed suit at the five or six level specifically asks partner whether he holds good trumps. So, if spades is the agreed suit, five hearts invites six spades and six hearts invites seven spades. With good trump holding, responder jumps to the next level in the agreed suit. Without good trumps, he bids the agreed suit at the same level.
Other features of the system include:
Weak no trump openings combined with one no trump constructive bid.
Bidding up the line with four card suits.
Five card suit requirement to respond 2 hearts to a 1 spade opening.
A bid of a third suit by partner is forcing.
Lead the ace from ace-king.
An immediate raise requires at least four card trump support.
Simple overcalls are strong and jump overcalls are weak.