[Lovera]

Hi. While I wasn't on BBO, I dedicated myself to verifying the weak jump bids (selecting the hands to play with repeated redeals or skipping positions until I reached the vulnerable position I requested). I was therefore able to see when I was GIB's partner that was in N that the partner in r vs w vulnerability bidded itself weak and not strong (but it seems that the robot always does this). I have therefore decided to open this topic of mine to clarify the by providing a qualified overview.

From th book Il libro completo del Bridge di gara by G. Barbone Home edit MURSIA pagg. 78-83:Chaptel X JUMP INTERFERENCE In relatively recent times, American school experts have argued that, in competitive bridge and in particular in pairs competitions, jump interference can be better exploited to disturb opponents and have established the use of interference jump with a weak hand.(...)In practice, the use of jump interference is regulated as follows by the authors who advocate it: - when you are vulnerable, jump interference indicates a strong hand; - when you are "not" vulnerable, jump interference indicates a weak hand.(...)Weak interference The limits for weak jump interference are subject to variations according to the different conceptions of the authors but, in addition to the common denominator which refers to the opportunity to use it only when one is not vulnerable, another common element is represented by the presence of "a good six-card suit from the possession of no more than an Ace or a King". The need to rigidly predetermine the requirements of the hand is intended to allow the partner, especially when he has not yet had the opportunity to speak, a fairly realistic assessment of the overall strength of the line. It follows that, when S has interfered with a jump in a non-vulnerable position, N must be certain that S's hand cannot possess an Ace or even a King: if this were the case, S would have had to interfere at the level and possibly repeat the his suit on the second turn. In other words, when weak jump overcall is used, any level overcall shows a stronger scoring hand and therefore at least 9-10 points.(Lovera)

[Lovera]

"Assuming that the bid was: East 1♦ South 2♠ the non-vulnerable S cards must be more or less: 1) ♠KJ10863 ♥852 ♦4 ♣Q103 Typically respects the requirements: a good six-card suit, only one King, limited scoring. 2) ♠QJ10854 ♥A32 ♦52 ♣87 The Ace or King contained in the hand can be in a different suit than the six-card suit that is mentioned and which, in any case, must be quite compact. 3) ♠KQJ864 ♥J2 ♦3 ♣ J864 Another hand from a typical overcall with weak jump interference. 4) ♠ K96432 ♥ 32 ♦ 42 ♣ KJ4 It can be considered at the limit as the presence of a second King compensates for the poverty of the sixth suit.


The desire to use weak jump interference or the concern of making bids at too high a level must not lead to errors in the evaluation of hands which appear equivalent but, vice versa, require different treatment. If E has opened with 1♦ and S, not vulnerable, has: 1) ♠ AJ10753 ♥ K63 ♦ 3 ♣ J86 The correct intervention is that of 1♠; interfering by saying 2♠ would feel like a poorer hand and could preclude any conclusion to the game or push for a phantom sacrifice. 2) ♠KQJ1086 ♥ 1083 ♦ 72 ♣ K8 The interference of 2♠ is to be excluded and it is preferable to name the suit at level one and repeat it on the next round. 3) ♠ KJ109753 ♥ 73 ♦2 ♣ Q102 The suit of ♠ is seven cards and determines a different evaluation. The hand lends itself better to a more effective interdictive action which can be made by bidding 3♠.(...)"

[Lovera]

Since the aim is to change the robot's bid from weak to strong when it is in the zone (=red) and opponents are white let's also see, for greater objectivity or ease of discussion, what the Stayman system says instead which I believe GIB for BBO does reference:

"The jump overcall. Typically, most players use three ways to show a good hand when an opponent opens the auction: they give an informative double, they call a no trump or they make a jump overcall. This last bid is splendid, but has the disadvantage of maintaining a magnificent bidding tool for a rather rare work. Our experience teaches us that the use of the strong jump overcall, made with strong hands, occurs on few occasions and even when these opportunities have arisen, an informative double, followed by the bid of a suit, has done equally well if no better. Since the strong jump call has little to gain by keeping it as a show strength bid, our system assigns it a function that puts it to work much more frequently and with greater usefulness, namely 1) as a call preventive, under equal conditions of vulnerability[=w vs w or r vs r] or when only the opponents are in the zone[=r vs w]; 2) to show a good hand when the overcaller is in the zone and the opponents are not[=r vs w]."(pagg.215-217).

[Lovera]

(continuation of # 3 - pages 215-217)" Vuln.: w vs w (42) ♠8 ♥63 ♦QJ10865 ♣KQJ2 1♠ ? You bid 3♦. - This hand should take 6-7 tricks, so it is unlikely to be heavily penalized. Your defensive maneuver done at a high level takes away a round of bidding from your opponents and allows your partner to make the remaining decisions. Vuln.: w vs r (43) ♠Q5 ♥763 ♦54 ♣KQJ1092 1♥ ? Bid 3♣ - You can take at least 5 tricks, but your honors will reduce the loss to 600 points maximum. In zone[=red] it would be a mistake to bid 3♣ with such a hand. Vuln.:r vs r (44) ♠8 ♥7 ♦A1098654 ♣QJ105 1♥ ? Bid 3♦ - This hand should make 7 tricks and the call is precise and descriptive. If the partner has something in ♣, you can even keep the contract. Vuln.:r vs w (45) ♠54 ♥K7 ♦AKQJ54 ♣A54 1♠ ? You bid 3♦. - Jump-calling in a minor suit, when you are in the zone[=red]and the opponents are not , shows a good suit and a good hand.Vuln.:w vs w (46) ♠KQ10864 ♥9 ♦QJ102 ♣85 1♥ ? Bid 2 ♠. - This is the classic jump overcall in such vulnerable conditions. Vuln.:w vs r (47) ♠QJ10854 ♥9 ♦QJ83 ♣65 1♣ ? Bid 2♠. - The hand is almost worthless in defense and the barrier can make it possible for you, with minimal sacrifice, to keep opponents away from their best contract. After the precise description of the hand any subsequent action should be left to the partner. Vuln.:r vs w (48) ♠AJ10954 ♥AQJ ♦863 ♣5 1♦ ? Bid 2 ♠. - Your hand is strong enough and the contribution of a few tricks will be sufficient for the game. You have 7 to 8 probable tricks. (8) ♠AKJ954 ♥KQ2 ♦853 ♣6 1♥ ? Double, unless you are in zone[=red] and your opponents are not, in which case bid 2♠. The jump overcall is preventive except in the one case indicated above. The overcaller therefore employs a combination of two bids - a double followed by a suit bid - to show the great strength of his hand.(... from page 250)Vuln.:r vs w (49) ♠AKJ54 ♥AQ1076 ♦95 ♣2 1♦ ? Bid 2♠. - Jump overcalling can be done with a two-suited hand when the contribution of one or two key cards will give a good game for the round."