message: Update DataFrame_join.tcc
  Fixed or
diff: @@ -18,7 +18,7 @@ template<typename RHS_T, typename ... types>
  StdDataFrame<TS> DataFrame<TS, HETERO>::
  join_by_index (const RHS_T &rhs, join_policy mp) const {
  - static_assert(std::is_base_of<StdDataFrame<TS>, RHS_T>::value or
  + static_assert(std::is_base_of<StdDataFrame<TS>, RHS_T>::value ||
  std::is_base_of<DataFrameView<TS>, RHS_T>::value,
  "The rhs argument to join_by_index() can only be "
  "StdDataFrame<TS> or DataFrameView<TS>");
  