answer.code:22:84: error: ‘conjunction_v’ is not a member of ‘std’
   22 |     template <typename ...Constraints> using constraints_t = std::enable_if_t<std::conjunction_v<Constraints...>, std::nullptr_t>;
      |                                                                                    ^~~~~~~~~~~~~
answer.code:22:84: note: ‘std::conjunction_v’ is only available from C++17 onwards
answer.code:22:84: error: ‘conjunction_v’ is not a member of ‘std’
answer.code:22:84: note: ‘std::conjunction_v’ is only available from C++17 onwards
answer.code:22:109: error: expected parameter pack before ‘...’
   22 |     template <typename ...Constraints> using constraints_t = std::enable_if_t<std::conjunction_v<Constraints...>, std::nullptr_t>;
      |                                                                                                             ^~~
answer.code:22:112: error: template argument 1 is invalid
   22 |     template <typename ...Constraints> using constraints_t = std::enable_if_t<std::conjunction_v<Constraints...>, std::nullptr_t>;
      |                                                                                                                ^
answer.code:25:44: error: ‘constraints_t’ was not declared in this scope
   25 |     template <typename T> struct bitnum<T, constraints_t<std::is_integral<T>>> { static constexpr int value = std::numeric_limits<std::make_unsigned_t<T>>::digits; };
      |                                            ^~~~~~~~~~~~~
answer.code:25:76: error: template argument 2 is invalid
   25 |     template <typename T> struct bitnum<T, constraints_t<std::is_integral<T>>> { static constexpr int value = std::numeric_limits<std::make_unsigned_t<T>>::digits; };
      |                                                                            ^~
answer.code:25:78: error: expected unqualified-id before ‘>’ token
   25 |     template <typename T> struct bitnum<T, constraints_t<std::is_integral<T>>> { static constexpr int value = std::numeric_limits<std::make_unsigned_t<T>>::digits; };
      |                                                                              ^
answer.code:31:57: error: ‘constraints_t’ was not declared in this scope
   31 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_signed<T>, is_nbit<T, 32>>> { using type = long long; };
      |                                                         ^~~~~~~~~~~~~
answer.code:31:103: error: wrong number of template arguments (3, should be at least 1)
   31 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_signed<T>, is_nbit<T, 32>>> { using type = long long; };
      |                                                                                                       ^~
answer.code:30:61: note: provided for ‘template<class T, class> struct suisen::safely_multipliable’
   30 |     template <typename T, typename = std::nullptr_t> struct safely_multipliable { using type = T; };
      |                                                             ^~~~~~~~~~~~~~~~~~~
answer.code:31:105: error: expected unqualified-id before ‘>’ token
   31 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_signed<T>, is_nbit<T, 32>>> { using type = long long; };
      |                                                                                                         ^
answer.code:32:57: error: ‘constraints_t’ was not declared in this scope
   32 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_signed<T>, is_nbit<T, 64>>> { using type = __int128_t; };
      |                                                         ^~~~~~~~~~~~~
answer.code:32:103: error: wrong number of template arguments (3, should be at least 1)
   32 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_signed<T>, is_nbit<T, 64>>> { using type = __int128_t; };
      |                                                                                                       ^~
answer.code:30:61: note: provided for ‘template<class T, class> struct suisen::safely_multipliable’
   30 |     template <typename T, typename = std::nullptr_t> struct safely_multipliable { using type = T; };
      |                                                             ^~~~~~~~~~~~~~~~~~~
answer.code:32:105: error: expected unqualified-id before ‘>’ token
   32 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_signed<T>, is_nbit<T, 64>>> { using type = __int128_t; };
      |                                                                                                         ^
answer.code:33:57: error: ‘constraints_t’ was not declared in this scope
   33 |     template <typename T> struct safely_multipliable<T, constraints_t<std::is_unsigned<T>, is_nbit<T, 32>>> { using type = unsigned long long; };
      |                                                         ^~~~~~~~~~~~~
answer.code:33:105: error: ...