/in/foo.cc: In function 'constexpr int Contor(const Matrix&)':
/in/foo.cc:19:1: error: body of constexpr function 'constexpr int Contor(const Matrix&)' not a return-statement
 }
 ^
/in/foo.cc: In function 'constexpr Matrix inv_cantor(int, int)':
/in/foo.cc:46:1: error: body of constexpr function 'constexpr Matrix inv_cantor(int, int)' not a return-statement
 }
 ^
/in/foo.cc: At global scope:
/in/foo.cc:49:20: error: 'bfs' function uses 'auto' type specifier without trailing return type
 constexpr auto bfs() {
                    ^
/in/foo.cc:49:20: note: deduced return type only available with -std=c++14 or -std=gnu++14
/in/foo.cc: In function 'constexpr auto bfs()':
/in/foo.cc:78:1: error: body of constexpr function 'constexpr auto bfs()' not a return-statement
 }
 ^