@Override
 public void printMalformedExpression(Appendable a, int flags) throws IOException {
   a.append("-(");
   if (negated == null) {
     a.append("null");
   } else {
     negated.print(a, flags);
   }
   a.append(')');
 }
 @Override
 public void print(Appendable a, int flags) throws IOException {
   a.append("-(");
   negated.print(a, flags);
   a.append(')');
 }