public void addValuePossibility(int valuePossibility) {
		if (valuePossibility < 1 || valuePossibility > 9) {
			throw new IllegalArgumentException("the value posibility should be between 1 and 9");
		}
			
		if (!this.valuePossibilities.contains(valuePossibility)) {
			this.valuePossibilities.add(valuePossibility);
		}
	}