sclass ThoughtSpace {
  new LinkedHashMap<S, LispStatement> statements;
  new HashSet<Lisp> statementsIndex;
  new LinkedHashMap<S, SimpleConcept> concepts;
  
  void addStatement(Lisp l) {
    if (!containsStatement(l)) {
      LispStatement s = new LispStatement(l);
      statements.put(s.globalID, s);
      statementsIndex.add(l);
    }
  }
  
  bool containsStatement(Lisp l) {
    ret statementsIndex.contains(l);
  }
}