static Sq findUniquePredecessor(Model model, Sq end) {
        ArrayList<Sq> preds = new ArrayList<Sq>();
        for (int x = 0; x < model.width(); x++) {
            for (int y = 0; y < model.height(); y++) {
                Sq other = model.get(x, y);
                if (other.connectable(end)) {
                    preds.add(other);
                }
            }
        }

        if (preds.size() == 1) {
            if (preds.get(0).sequenceNum() > 0 && end.sequenceNum() > 0) {
                if (preds.get(0).sequenceNum() + 1 == end.sequenceNum()) {
                    return preds.get(0);
                } else {
                    return null;
                }
            }
            return preds.get(0);
        }
        return null;
    }

	static Sq findUniqueSuccessor(Model model, Sq start) {
        ArrayList<Sq> succs = new ArrayList<Sq>();
        for (int x = 0; x < model.width(); x++) {
            for (int y = 0; y < model.height(); y++) {
                Sq other = model.get(x, y);
                if (start.connectable(other)) {
                    succs.add(other);
                }
            }
        }

        if (succs.size() > 0
                && succs.get(0).sequenceNum() > 0
                && start.sequenceNum() > 0) {
            return succs.get(0);
        }

        if (succs.size() == 1) {
            return succs.get(0);
        }
        return null;
    }