Negative Doubles

Board 1
North Deals
N-S Vul
♠K Q 8 4
♥8
♦A 10 4 3
♣K J 9 8
♠9 7 6
♥Q J 7
♦8 7 6 5
♣4 3 2
N
WE
S
♠3 2
♥A K 10 5 3
♦K 9 2
♣Q 10 7
♠A J 10 5
♥9 6 4 2
♦Q J
♣A 6 5
WestNorthEastSouth
 1♦11♥2Dbl3
Pass2♠4Pass4♠
All pass   
  1. N opens the bidding 1♦
  2. E has a good ♥ overcall
  3. S has enough points for game. By using a negative double S can show a 4 card spade suit.
  4. When N bids 2♠, S can bid game.
4♠ by North