This hand came up in a f2f team of 4 club league match. We were playing a 15-17 5 card major system with no check back agreement. The bidding with opps silent me sitting east went:
1♣- 1♦-1♠-2♠
Trumps broke 3-3 and I made 10 tricks but lost 6 imp as opps playing Acol bid 3NT making an overtrick. I was not very happy with my partner bidding 2♠, but can see that she certainly had a problem with her next bid. We are a fairly regular partnership and I did have in mind introducing the idea of a check-back arrangement but decided to defer this until something went wrong with our present up-the-line method and could demonstrate why a check-back system was superior.
However, as far as I can see, the only system that easily reaches 3NT is Acol. 1♣-1♦-1♠-3♣-3NT. In Acol a 1NT response is 6-9, 10 points being too strong and since a 1♣ opening bid guarantees 4 card, west with 10 points and 8 losers can raise to 3♣; thus setting up the 3NT bid from east.
Looking at all other systems in the BBO FD files, I cannot legitimaely get to 3NT.
1♣-1NT- pass or 1♣-1♦-1♠- ? . I would like to have been able to argue that if you rebid all balanced 12-14 hands with 1NT, then 1♣-1♦-1♠ has to be unbalanced with at least 5♣+4♠. Unfortunately this is not the case (or at least not spelt out). The rebid of 1♠ in:
BBO Adv = non forcing 4+♠
BBOITA = 3+♣ 4♠
Bridge base basic = 4♠
majeur 5 ieme = no 4 cards in ♥
It looks like that if you cannot respond 1♦ because you are balanced with no 4 card major, then you have to respond 1NT 6-10. Thus making any bid except pass highly speculative. If the system allows you to respond 1♦, then is a rebid of 1♠ unbalanced? If it can be taken to be so then balanced hands rebid 1NT.
The problem here is that 1♣-1♦-1NT-2♣ is natural in BBOAdv and Bridgebase basic. BBOITA says 2♣ is forcing, majeur 5ieme says natural (or check-back if playing Walsh).
OK I can recommend a simple check-back 2♣ to my partner after 1♣-1♦-1NT. This begs the question of what to recommend after 1♣-1♥-1NT or 1♣-1♠-1NT. I like 2-way check-back but hesitate to introduce the memory load after having already introduced quite a few gadgets. My partner is a good player but seems to prefer creative bidding in problem situations rather than formal artificial bids. So I think I am leaning to a simple 2♣ in all situations. Viva Italia!
BTW My partner said that she could not respond 3♣ with her 2nd bid since I might only have 3♣, which of course is true with up-the-line bidding.

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