@Override
    public boolean add(E o) {
        Node<E> prev = head;
        while (prev.next != null) {
            int comp = compare(o, prev.next.value);
            if (comp < 0) {
                prev.next = new Node<>(o, prev.next);
                size++;
                return true;
            } else if (comp == 0) {
                return false;
            }
            prev = prev.next;
        }
        // if we haven't returned yet, this is greater than
        prev.next = new Node<>(o, null);
        size++;
        return true;
    }
@see java.util.AbstractCollection#add(java.lang.Object)
src/nu/validator/collections/HeadBiasedSortedSet.java