namespace boost {
  namespace dataflow {
    namespace utility {
      template<typename T, typename Result = void> struct enable_if_type;
      template<typename T0 = void_, typename T1 = void_, typename T2 = void_, 
               typename T3 = void_, typename T4 = void_, typename T5 = void_> 
        struct all_of;
    }
  }
}