[Kungsgeten]

One Swedish pair in the Bermuda Bowl used something like the following opening structure:

1C = 16+
1D = 12-15 NT or 10-15 4M and a minor
1M = 5+M 10-15
1NT = Both minors 10-15
2m = 6+ suit, 10-15

To me it seems more obvious to use 1NT as 12-15 NT and make 1D unbalanced (if you're okay with opening 1C on 16 flat). What do you think is the reason behind their choice? Could it be that the weak NT is better off opening a nebulous diamond (responder can search for a major fit at a lower level)?

[nullve]

http://info.ecatsbri...ne-Bergdahl.pdf

[mgoetze]

 Kungsgeten, on 2016-January-21, 17:00, said:

Could it be that the weak NT is better off opening a nebulous diamond (responder can search for a major fit at a lower level)?

Yes, I have played something similar and this is pretty much the reason.

[rbforster]

 Kungsgeten, on 2016-January-21, 17:00, said:

1D = 12-15 NT or 10-15 4M and a minor
1NT = Both minors 10-15

To me it seems more obvious to use 1NT as 12-15 NT and make 1D unbalanced...

If 1D doesn't promise diamonds, balanced or otherwise, it's much much more annoying to reach minor partials accurately. Take an auction like 1D-1M-2C. in standard that would show both minors and no major fit, so responder could preference to his better minor. In this method, it would probably show clubs and 4OM (and not diamonds). But if 1D could be both minors or just 1 minor and a misfitting major, how will responder know when to play in diamonds? Plus, 1N for both minors can stop easily in 2m right away.

[Kungsgeten]

 rbforster, on 2016-January-22, 22:09, said:

If 1D doesn't promise diamonds, balanced or otherwise, it's much much more annoying to reach minor partials accurately. Take an auction like 1D-1M-2C. in standard that would show both minors and no major fit, so responder could preference to his better minor. In this method, it would probably show clubs and 4OM (and not diamonds). But if 1D could be both minors or just 1 minor and a misfitting major, how will responder know when to play in diamonds? Plus, 1N for both minors can stop easily in 2m right away.

Well I meant that 1D could show an unbalanced hand with diamonds, not any unbalanced hand. I do not think it is a good idea to play it as "any unbalanced hand without a five card major" (but Marshall Miles did in his Unbalanced Diamond system), but it would probably be okay if single-suited minor hands were excluded. Then:

1D--1H;
1S = Spades
1N = Both minors
2m = That minor + hearts
2H = Both minors, 3 hearts

1D--1S;
1N = Both minors
2m = That minor + hearts
2H = 4 spades
2S = 3 spades

[rbforster]

 Kungsgeten, on 2016-January-23, 08:02, said:

Well I meant that 1D could show an unbalanced hand with diamonds, not any unbalanced hand.

Ok, but then 5C/4M hands have to go back into a precision style 2C, which is presumably what they were trying to avoid by having a 2m opening promise 6+. The structure in OP let's you put both m+M minor hands into 1D and handle things reasonably well, at least barring competition, while having both minors in there as well or in place of a balanced option, is much more problematic.