public String toString() {
		String s = "";
		s += "(" + xx + ", " + yy + "): " + getal + " b: " + bekend + ", g: " + gevuld + "\t";
		for (int h=0; h<3; h++) {
			for (int w=0; w<3; w++) {
				s += (omgeving[w][h] == null ? "." : (omgeving[w][h] ? "1" : "0"));
			}
			if (h<2) s += " ";
		}
		return s;
	}