template < class >
  struct repack;

  template<template<typename...> class T, typename... Args>
  struct repack< T<Args...> > {

    template < template<class...> class U >
    using type = U<Args...>;
  };

  template < typename From, template < class ... > class To >
  using repack_t = typename repack<From>:: template type<To>;