what's wrong with this alpha-beta tree??

From: alessandro (halex2000_at_virgilio.it)
Date: 08/28/04 

Date: Sat, 28 Aug 2004 15:15:16 GMT

Hi, these are the two functions of my alpha-beta tree:
  protected int Max(Board b, Board oldb, int alpha, int beta, int depth)
  {
    int tmp = b.CheckForVictory(); //Check for the end of the game
    if(tmp == 1) return 1000; //Max wins
    else if(tmp == 2) return -1000; //Min wins

    if(depth == 0) return EvaluateGame(b, oldb); // We reached the max tree
depth

    Board child = new Board();
    for(int x = 0; x < 6; x++)
      for(int y = 0; y < 5; y++)
    {
      if(!b.Verify(x, y, true)) continue; //The move is not valid
      child.CopyFrom(b);
      child.AddFast(x, y, true);

      tmp = Min(child, b, alpha, beta, depth-1); //Recursive call
      if(tmp > alpha)
      {
        alpha = tmp;
        _x = x;
        _y = y;
      }
      if(beta < alpha) return beta;
    }
    return alpha;
  }

  protected int Min(Board b, Board oldb, int alpha, int beta, int depth)
  {
    int tmp = b.CheckForVictory(); //Check for the end of the game
    if(tmp == 1) return 1000; //Max wins
    else if(tmp == 2) return -1000; //Min wins

    if(depth == 0) return -EvaluateGame(b, oldb); // We reached the max tree
depth

    Board child = new Board();
    for(int x = 0; x < 6; x++)
      for(int y = 0; y < 5; y++)
    {
      if(!b.Verify(x, y, true)) continue; //The move is not valid

      child.CopyFrom(b);
      child.AddFast(x, y, true);

      tmp = Max(child, b, alpha, beta, depth-1); //Recursive call
      if(tmp < beta)
      {
        beta = tmp;
        _x = x;
        _y = y;
      }

   if(beta < alpha) return alpha;
    }
    return beta;
  }

I call them with the following instruction:
        Max(b, oldb, -100000, 100000, tree_depth);

But my game doesn't notice that with only one move it would win. Is this
code wrong?
NOTE: EvalGame() returns a value that estimates how the game state is good
FOR MAX.
Thank you!

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