return ibmToPenn(Sexp.read(tok, '[', ']'));
Sexp raw = Sexp.read(tok, '[', ']'); return raw == null ? null : ibmToPenn(raw);
  public static Sexp readIbmTree(SexpTokenizer tok) throws IOException {    return ibmToPenn(Sexp.read(tok, '[', ']'));  }