anchor.diff:  
     int mineCount(int x, int y) {
       int count = 0;
  -    int my = cols - 1;
  -    int mx = rows - 1;
  -
  -    count += x > 0 ? bombs(x - 1, y) : 0;
  -    count += x < mx ? bombs(x + 1, y) : 0;
  -    count += y > 0 ? bombs(x, y - 1) : 0;
  -    count += y < my ? bombs(x, y + 1 ) : 0;
  -
  -    count += (x > 0) && (y > 0) ? bombs(x - 1, y - 1) : 0;
  -    count += (x < mx) && (y < my) ? bombs(x + 1, y + 1) : 0;
  -    count += (x < mx) && (y > 0) ? bombs(x + 1, y - 1) : 0;
  -    count += (x > 0) && (y < my) ? bombs(x - 1, y + 1) : 0;
  -
  +    count += bombs(x - 1, y);
  +    count += bombs(x + 1, y);
  +    count += bombs(x, y - 1);
  +    count += bombs(x, y + 1 );
  +    count += bombs(x - 1, y - 1);
  +    count += bombs(x + 1, y + 1);
  +    count += bombs(x + 1, y - 1);
  +    count += bombs(x - 1, y + 1);
       return count;
     }
   
  -  int bombs(int x, int y) {
  -    return cells[y][x] ? 1 : 0;
  -  }
  +  int bombs(int x, int y) => inBoard(x, y) && cells[y][x] ? 1 : 0;
  +
  +  bool inBoard(int x, int y) =>
  +    (x > 0 && x < (cols - 1) && y > 0 && y < (rows -1));
   }
   
   Widget buildCell(Widget child) {
  
positive.code:     }
      return buildCell(buildInnerCell(text));
    }
  
  }
  
  void main() {
  
negative.code: 
    // Recursively uncovers cells whose totalMineCount is zero.
    void cull(int x, int y) {
      if (!inBoard(x, y))
        return;
      if (uiState[y][x] == CellState.cleared)
        return;
      uiState[y][x] = CellState.cleared;
  