code: static boolean isRelationalOperation(Node n) {
      switch (n.getToken()) {
        case GT: // equal
        case GE: // not equal
        case LT: // exactly equal
        case LE: // exactly not equal
          return true;
        default:
          break;
      }
      return false;
    }
docs: Returns true if the operator on this node is relational.
  the returned set does not include the equalities.