text: #ifndef FWD_TYPELIST_BACK_H
  #define FWD_TYPELIST_BACK_H
  
  #include "TypeList.h"
  #include "TypeSet.h"
  
  namespace aether {
  
  struct back_t {
    template <typename... Ts>
    constexpr auto operator()(TypeList<Ts...>) const;
  
    template <typename... Ts>
    constexpr auto operator()(TypeSet<Ts...>) const;
  };
  
  constexpr back_t back{};
  
  } // end namespace aether
  
  #endif
  