Negative Doubles

Board 2
East Deals
E-W Vul
J 7
J 5 2
9 8 7 5 3 2
9 4
Q 10 9 4
Q 9 8 7
A
A 10 8 3
N
WE
S
A 6 5 2
3
K Q J 6
Q J 7 6
K 8 3
A K 10 6 4
10 4
K 5 2
WestNorthEastSouth
  1112
Dbl3Pass2Pass
44All pass  
  1. E opens 1
  2. S overcalls 1
  3. W uses a negative double to show his 4 spades
  4. After E shows a fit and minimum response, W bids game
4 by East