docs: public Expression2 getLogicalForm() {
      Expression2 preUnaryLogicalForm = getPreUnaryLogicalForm();
      if (unaryRule == null) {
        return preUnaryLogicalForm;
      } else if (preUnaryLogicalForm == null || unaryRule.getUnaryRule().getLogicalForm() == null) {
        return null;
      } else {
        return Expression2.nested(unaryRule.getUnaryRule().getLogicalForm(), preUnaryLogicalForm);
      }
    }