sclass ActualThoughtSpace extends AbstractThoughtSpace {
  new TripleIndex index;
  int limit; // 0 = no limit
  Map<TripleWeb, Bool> blocked = newWeakHashMap();
  Set<S> blockedA;

  *() {}
  *(int *limit) {}
  *(AbstractThoughtSpace parent) { super(parent); }
  
  // existence of triple has already been checked
  public GlobalID postTriple(T3<S> t) {
    if (limitReached()) fail("Thought space limit reached");
    TripleWeb w = tripleWeb(t);
    index.addTriple(w);
    ret w.globalID();
  }
  
  bool limitReached() {
    ret limit > 0 && size() >= limit;
  }
  
  L<TripleRef<S>> get(S s) {
    ret ai_triplesToTripleRefs_lazyList(s, getTriples(s));
  }
  
  L<TripleWeb> getTriples(S s) {
    L<TripleWeb> l = filterNonBlockedTriples_lazy(parent.getTriples(s));
    ret combineLists(l, index.getTriples(ai_shortenForIndex(s)));
  }
  
  L<TripleWeb> filterNonBlockedTriples_lazy(final L<TripleWeb> l) {
    class FilterList extends LazyList<TripleWeb> {
      final int n = l(l);
      public int size() { ret n; }
      public TripleWeb get(int i) {
        TripleWeb w = syncGet(l, i);
        if (w != null && isBlocked(w)) null;
        ret w;
      }
    }
    ret new FilterList;
  }
  
  L<TripleWeb> filterNonBlockedTriples(L<TripleWeb> l) {
    if (empty(blockedA)) ret l;
    L<TripleWeb> out = emptyListWithCapacity(l);
    for (TripleWeb w : l)
      if (!isBlocked(w))
        out.add(w);
    ret out;
  }
  
  bool isBlocked(TripleWeb t) {
    ret contains(blockedA, t.a);
  }
  
  int size() { ret index.size(); }
}