The origin of this call of double is unknown, but it has been rumored to be a double employed at colleges and universities, especially in The Netherlands. The origin for the designation for this double is also unknown, but is believed to be the surname of a bridge player and has no relation to the lebensohl conventional method. Source is from website for the M.A.F. (MAF) Bidding System located on the web and in The Netherlands.
The fundamental concept is illustrated in the example and bidding auction below.
South West North Meaning 1 1 West has overcalled in the higher-ranking Major suit, strongly indicating a 5-card Spade suit. Double The Sohl Double.
KJ74 75 Q103 J985
In this bidding sequence the double, per partnership agreement, does not mean a Support Double for the Heart suit of partner. The double does not, again per partnership agreement, show the two unbid Minor suits.
The Sohl Double means only that the doubler also has a 4-card Spade suit, and that the doubler intended to bid Spades originally if West had not bid Spades instead.
The Sohl Double, however, does communicate the information that the doubler has absolutely no support for the suit of partner, meaning two or fewer Hearts. The pattern of the doubler, therefore, could be: 4 Spades - 2 Hearts - 3 Diamonds - 4 Clubs, or 4-1-4-4.
The conventional method of the Sohl Double is normally limited to only this particular bidding sequence. However, per partnership agreement, both Minor suit openings followed by a Major suit overcall may be included as bidding sequences.
If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.