Fuente: http://taigabridge.net/

In this article we will see the value of paying attention to the vulnerability and working together with your partner to obstruct the opponents. When people hear the word «preempt» they immediately think of 3-level opening bids. But there is another kind of preempt, called a «cooperative preempt»: a partnership realizes that its combined assets include nine, ten or more of a suit and few enough high cards that the opponents almost surely have a game.

Here is a hand illustrating this idea:Mano Bower

South opens a routine 1, and West starts with a takeout double, intending to raise whichever suit East chooses.

Did you look at North’s cards, count 2 HCP, and automatically pass? If you were vulnerable and your opponents were not, being cautious would be wise. But you know your side has at least 9 spades and is likely to have less than half the high cards. This is your one chance to tell your partner. North can jump to 3! (Unlike 1-Pass-3, which would promise a good hand, South knows that the jump to 3 is based on distribution, not high cards; if North had a 10-HCP hand, he would either redouble, or make some kind of conventional strong raise.)

If North had passed, East would bid 2; if North had bid only 2, East probably would try 3. But over 3, East is afraid to bid.

Now it is South’s turn: South has a sixth spade and a singleton heart — and is, therefore, the only person at the table who is sure that E-W can probably make 4 and N-S have a ten-card spade fit. Raise to 4, and don’t care about whether you make it! Your partner will usually have six points, not two – but if North has enough to set 4, he has enough that you will make 4.

West, with a monster hand, can only double 4 and collect a lousy 100-point penalty, winning a heart, two diamonds, and a club, instead of making five in hearts.