[Dinarius]

Non-Vul against Vul, in the second seat, you hold........

♠K,Q,J,10,2
♥6,3
♦A,K,Q,7,6,4
♣

Dealer on your right opens ♣3.

Over to you....

Thanks.

D.

[Cyberyeti]

4♦ diamonds and a major at least 5-5 ? (we play it forcing but not everybody does)

[helene_t]

4♣ showing diamonds and a major is better.

If you don't have that agreement I bid 3♦. I can see a case for double or 3♠ also.

[LAVENDERi]

I will take a view on probability. Frist, we don't know what your p have. Your p can support any suit.
(1)Double：There are 2 chances for your p to support your suits - diamonds or spades.
(2)3D：your p doesn't always support your diamonds.

It seems like double is a better bid. But you may consider what if your p bid 4H? Then you two are just unlucky. And that's how preempt bids interfers the bidding.

[ggwhiz]

If you don't play 4♦ as showing this kind of hand (which I don't) 4♣ shows any 2 suiter and you can convert 4♥ to spades.

Naturally, you will belong in 4♥ but thems the breaks.

[kenrexford]

You are all wrong. Flags here. 4♣ as diamonds plus hearts, 4♦ as diamonds plus spades. Duh!

[Cyberyeti]

kenrexford, on 2016-January-20, 14:46, said:

You are all wrong. Flags here. 4♣ as diamonds plus hearts, 4♦ as diamonds plus spades. Duh!

So what do you do with a) both majors, b) a hand that wants to bid a "to play" 4M

[kenrexford]

Cyberyeti, on 2016-January-20, 15:01, said:

So what do you do with a) both majors, b) a hand that wants to bid a "to play" 4M

Two options. First, double and then bid 4C if needed, like over 3NT or 3D. Second, you can make 4C reds or majors, planning to correct 4D to 4H.

If 4C shows diamonds and a major, with 4D as both majors, Advancer can only probe the major with a fit for either, or Overcaller must be able to force game. Plus, Advancer is limited to an ability to show very long hearts.

If 4D shows diamonds and spades, Responder can handle very long hearts, by bidding 4H. If 4C shows reds or majors, 4S shows very long spades, so Advancer never has a problem with a very long suit. Plus, both 4C and 4D always promise one of the majors, 4D obviously spades, but 4C always hearts. So, Advancer only needs one fit to move, and he always knows where to go.

The problem most aroses if Responder bids 5C, to some degree. While this might be minor, 5H scores better than 5D. In the diamonds-or-major scheme, Advancer has a known fit in one sequence in either major, in the other in diamonds only. In 4C as hearts and another, Responder knows two possible fits in one sequence, diamonds or spades, and always knows hearts in the other. Thus, by rough calculations, it seems we know of 1 spade fit, 1 heart fot, and 2 diamond fits in the former, 1 diamond, 1 spade, and 2 hearts in the latter, which inproves our total gains slightly.

The other benefit is by a passed hand. 4D as majors and 4C as clubs plus a major leaves nothing idle. P-3C-4D-? as diamonds+spades leaves 4H idle, and thus a power 4S call.

[nige1]

Dinarius, on 2016-January-18, 08:50, said:

Non-Vul against Vul, in the second seat, you hold ♠ K,Q,J,10,2 ♥ 6,3 ♦ A,K,Q,7,6,4 ♣ -. Dealer on your right opens 3♣. Over to you....

IMO, if you have an agreement that 4m could show this kind of 2-suiter, then you should bid it. Otherwise you might try 3♦ (unlikely to be passed out) with the intention of bidding ♠ later.