Wikipedia
Rubensohl (also referred to as Rubinsohl) is a bridge convention that can be used to counter an opponent's intervention over a 1NT opening bid. After opponent's two-level overcall, all bids starting from 2NT are transfer bids to the next strain.
Although Ira Rubin devised similar methods before, the Rubensohl convention is attributed to Bruce Neill who described Rubensohl as an alternative to the Lebensohl convention in a Bridge World article in 1983.
When playing Rubensohl, the following applies after an opposing 2 (natural) overcall over partner's 1NT opening:
1NT - (2) - ??
dbl : penalty 2/ : to play 2NT : transfer to 3 3 : transfer to opponent's suit -> asks for four card major 3 : transfer to hearts (at least invitational) 3 : transfer to spades (at least invitational) 3 : transfer to 3NT -> game values but no major suit and no stopper in opponent's suit 3NT : to playSimilar schedules apply following a natural two-level overcall in any of the other suits.
Unlike Lebensohl, the partner of the 1NT opener can indicate his long suit at the first bid; this can be advantageous in competitive auctions.
The same transfer schedule can also be used following a conventional overcall over 1NT as long as this overcall indicates an anchor suit. For instance: following an Asptro 2 overcall (showing and another suit) over partner's 1NT opening, the bids 2NT, 3 and 3 would be transfers to the next strain, whilst 3 would be an asking bid.
Partnerships that have agreed to use Rubensohl often extend its use to include responses to partner's takeout double over an opposing weak two opening. For instance:
(2) - dbl - (pass) - ??
pass = penalty 2 : to play 2NT : transfer to clubs (weak or strong) 3 : transfer to diamonds (weak or strong) 3 : asking bid 3 : transfer to spades (at least invitational) 3 : transfer to 3NT -> game values but no major suit and no stopper in opponent's suit 3NT : to play