public Object becomeRoot(Token newRoot, Object oldRoot) {
   Object n = this.create(newRoot);
   adaptor.becomeRoot(n, oldRoot);
   dbg.becomeRoot(newRoot, oldRoot);
   return n;
 }
 public Object becomeRoot(Object newRoot, Object oldRoot) {
   Object n = adaptor.becomeRoot(newRoot, oldRoot);
   dbg.becomeRoot(newRoot, oldRoot);
   return n;
 }