src/main/java/org/organicdesign/fp/collections/PersistentTreeSet.java
@Override public ImSortedSet<E> tailSet(E fromElement) {
        return PersistentTreeSet.ofMap(impl.tailMap(fromElement));
    }
@Override public ImSortedSet<E> tailSet(E fromElement) {
        return PersistentTreeSet.ofMap(impl.tailMap(fromElement));
    }
{@inheritDoc}