4. Transfer Extensions
Transfer extensions are a method where, over a standard Jacoby transfer, responder's second bid is another transfer (to at least a 4-card suit/notrump). They allow the partnership to have more descriptive sequences at the 3-level, at the cost of two specific auctions.
The two auctions lost are the natural calls directly above the Jacoby transfers - so 1NT-2
♦*; 2
♥-2
♠ (standard: 4
♠5
♥ invitational NF) and 1NT-2
♥*; 2
♠-2NT (standard: 5
♠332, invitational NF). As the link above explains, the default way of handling this with Transfer Extensions is to downgrade the invitational 4
♠5
♥ hands into Garbage Stayman, or upgrade them to game forcing, and bid them accordingly. The 5
♠332 hand is shown through the artificial 'Spademan' sequence 1NT-2
♣* (Stayman); 2
♦*/2
♥-2
♠, showing exactly 5
♠332 invitational NF (if partner shows 4(+) spades we raise/blast to game).
The corresponding start to a Jacoby transfer in mini-Heeman is the relay auction 1NT-2
♣; 2
♦ - showing responder's hearts - or 1NT-2
♣; 2
♦-2
♥; 2
♠ showing spades. Despite the name 'transfer extensions' this convention does
not apply after mini-Heeman transfers, but only after the relay. They can be incorporated in the same way as standard, and you can keep all followup treatments the same way as standard.
There are some small differences though - by taking some of the advice from the previous section, we already have other options for the 5M332 hand types (i.e. bid them through the transfer, reasoning that the 5-3 fit plays well in 2NT opposite a minimum, or use the artificial superaccept after 1NT-2
♣; 2
♦-2
♥; ?). Mini-Heeman with transfer extensions can therefore use the sequence 1NT-2
♣; 2
♦-2
♠ to show 4
♠5
♥ inv NF (since there is no need for a transfer to notrump), and play transfer extensions over 1NT-2
♣; 2
♦-2
♥; 2
♠ without downside (depending on choice responder is never 5M332 or opener has shown a 2-card spade suit with a minimum so 5M332 invitational can downgrade and pass). Alternatively the bid 1NT-2
♣; 2
♦-2
♠ can be used as an artificial bid, doubling up on sequences starting at the 3-level or showing a different hand type. Note that mini-Heeman is not compatible with Garbage Stayman, so downgrading invitational 4
♠5
♥ hands forces responder to transfer to hearts and give up on the spades.
Lastly the traditional approach to transfer extensions treats them as forcing to game, citing the value-showing bids on the 3-level as their main benefit. Personally I think there is room for making these extensions invitational+, letting opener bid 3M with a major suit fit, accept the transfer with a hand not very suitable for either suit and make a value-showing bid setting the minor suit as trumps otherwise. Alternatively you could use artificial or swapped responses to save bidding space (e.g. show min/max, with major suit fit/no major suit fit but excited for the minor suit/neither).