private Area createArea(int aTile, boolean aProbability)
	{
		int flags = 0;
		TileSet areaTiles = new TileSet(mField);
		for (int tile : mField.getBorderOf(aTile))
		{
			MaskValue mask = mField.getMaskValue(tile);
			if (mask.isFlag()) flags++ ;
			else if ( !mask.isOpen() && !mask.isQuestion()) areaTiles.add(tile);
		}
		Area area = new Area(mField, mField.getTile(aTile) - flags, aProbability);
		area.addAll(areaTiles);
		return area;
	}