sclass ThoughtSpace {
  S globalID;
  new LinkedHashMap<S, LispStatement> statements;
  new HashMap<Lisp, LispStatement> statementsIndex;
  new LinkedHashMap<S, SimpleConcept> concepts;
  long changes;
  
  *() {}
  *(S *globalID) {}
  
  void addStatements(L<Lisp> l) { for (Lisp x : l) addStatement(x); }
  void addLispStatements(Collection<LispStatement> l) {
    for (LispStatement x : l) addStatement(x);
  }
  
  void addStatement(Lisp l) {
    if (!containsStatement(l)) addStatement(new LispStatement(l));
  }
  
  void addStatement(LispStatement s) {
    statements.put(s.globalID, s);
    statementsIndex.put(s.term, s);
    ++changes;
  }
  
  void removeStatement(S statementID) {
    removeStatement(statements.get(statementID));
  }
  
  void removeStatement(LispStatement s) {
    if (s != null) removeStatement(s.term);
  }
  
  void removeStatement(Lisp l) {
    LispStatement s = statementsIndex.get(l);
    if (s != null) {
      statements.remove(s.globalID);
      statementsIndex.remove(l);
      ++changes;
    }
  }
  
  bool containsStatement(Lisp l) {
    ret statementsIndex.containsKey(l);
  }
}