sclass ThoughtSpace {
  new LinkedHashMap<S, LispStatement> statements;
  new HashMap<Lisp, LispStatement> statementsIndex;
  new LinkedHashMap<S, SimpleConcept> concepts;
  
  void addStatement(Lisp l) {
    if (!containsStatement(l)) {
      LispStatement s = new LispStatement(l);
      statements.put(s.globalID, s);
      statementsIndex.put(l, s);
    }
  }
  
  void removeStatement(LispStatement s) {
    removeStatement(s.term);
  }
  
  void removeStatement(Lisp l) {
    LispStatement s = statementsIndex.get(l);
    if (s != null) {
      statements.remove(s.globalID);
      statementsIndex.remove(l);
    }
  }
  bool containsStatement(Lisp l) {
    ret statementsIndex.containsKey(l);
  }
}