main2.cpp: In function 'int main()':
main2.cpp:13:11: error: no match for 'operator-' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   13 | cout << a - b << endl;
      |         ~ ^ ~
      |         |   |
      |         |   basic_string<[...]>
      |         basic_string<[...]>
In file included from /usr/include/c++/12/string:47,
                 from /usr/include/c++/12/bitset:47,
                 from cmpslib19.h:4,
                 from main2.cpp:3:
/usr/include/c++/12/bits/stl_iterator.h:621:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  621 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/12/bits/stl_iterator.h:621:5: note:   template argument deduction/substitution failed:
main2.cpp:13:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   13 | cout << a - b << endl;
      |             ^
/usr/include/c++/12/bits/stl_iterator.h:1778:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1778 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/12/bits/stl_iterator.h:1778:5: note:   template argument deduction/substitution failed:
main2.cpp:13:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   13 | cout << a - b << endl;
      |             ^