@Override
    public Traverser.Admin<S> remove() {
        final Traverser.Admin<S> removed = super.remove();
        index.removeMapping(indexingFunction.apply(removed.get()), removed);
        return removed;
    }
Gets a collection of {@link Traverser} objects that contain the specified value.

@param k the key produced by the indexing function
@return
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/traverser/util/IndexedTraverserSet.java