@Main public void main() {
_subjects = new HashSet<String>();
_targets = new HashSet<String>();
RDFGraph G = new RDFGraph(new RDFGraph.TripleFile(_fn)); // FIXME: URIs uninitialized!
List<URI> uris = new ArrayList<URI>();
for (int subj_ix=0; subj_ix < G._n_subj2pred2obj.size(); subj_ix++) {
String subject = uris.get(subj_ix).stringValue();
SortedMap<Integer, SortedSet<Integer>> subj = G._n_subj2pred2obj.get(subj_ix);