answer.code:183:105: error: ‘requires’ only available with ‘-std=c++20’ or ‘-fconcepts’
  183 | template <class T, size_t size = std::tuple_size<T>::value> std::string to_debug(T, std::string s = "") requires(not std::ranges::range<T>);
      |                                                                                                         ^~~~~~~~
answer.code:183:123: error: ‘std::ranges’ has not been declared
  183 | template <class T, size_t size = std::tuple_size<T>::value> std::string to_debug(T, std::string s = "") requires(not std::ranges::range<T>);
      |                                                                                                                           ^~~~~~
answer.code:183:138: error: expected primary-expression before ‘>’ token
  183 | template <class T, size_t size = std::tuple_size<T>::value> std::string to_debug(T, std::string s = "") requires(not std::ranges::range<T>);
      |                                                                                                                                          ^
answer.code:183:139: error: expected primary-expression before ‘)’ token
  183 | template <class T, size_t size = std::tuple_size<T>::value> std::string to_debug(T, std::string s = "") requires(not std::ranges::range<T>);
      |                                                                                                                                           ^
answer.code:184:22: warning: use of ‘auto’ in parameter declaration only available with ‘-std=c++20’ or ‘-fconcepts’
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                      ^~~~
answer.code:184:30: error: ‘requires’ only available with ‘-std=c++20’ or ‘-fconcepts’
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                              ^~~~~~~~
answer.code:184:60: error: expected primary-expression before ‘&’ token
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                                                            ^
answer.code:184:62: error: ‘os’ was not declared in this scope; did you mean ‘cos’?
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                                                              ^~
      |                                                              cos
answer.code:184:39: error: there are no arguments to ‘requires’ that depend on a template parameter, so a declaration of ‘requires’ must be available [-fpermissive]
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                                       ^~~~~~~~
answer.code:184:39: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
answer.code: In function ‘std::string to_debug(auto:1)’:
answer.code:184:68: error: ‘os’ was not declared in this scope; did you mean ‘cos’?
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                                                                    ^~
      |                                                                    cos
answer.code:184:77: warning: no return statement in function returning non-void [-Wreturn-type]
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                                                                             ^
answer.code: At global scope:
answer.code:184:79: error: expected unqualified-id before ‘{’ token
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |                                                                               ^
answer.code:185:27: error: ‘std::string to_debug’ redeclared as different kind of entity
  185 | std::string to_debug(std::ranges::range auto x, std::string s = "") requires(not std::is_same_v<decltype(x), std::string>) {
      |                           ^~~~~~
answer.code:184:13: note: previous declaration ‘template<class auto:1> std::string to_debug(auto:1)’
  184 | std::string to_debug(auto x) requires requires(std::ostream& os) { os << x; } { return static_cast<std::ostringstream>(std::ostringstream() << x).str(); }
      |             ^~~~~~~~
answer.code:18...