public List<Element> getElementsOnPosition(Position position) {
		if (!validPosition(position))
			throw new IllegalArgumentException("The given position isn't valid!");

		List<Element> posElements = new ArrayList<Element>();

		for (Element element : elements) {
			if (element.getPositions().contains(position))
				posElements.add(element);
		}

		return Collections.unmodifiableList(posElements);
	}