foo.cc: In lambda function:
foo.cc:101:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  101 |             for (int i = 0; i < a.size(); i++) {
      |                             ~~^~~~~~~~~~
foo.cc:102:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  102 |                 for (int j = 0; j < b[0].size(); j++) {
      |                                 ~~^~~~~~~~~~~~~
foo.cc:103:39: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  103 |                     for (int l = 0; l < a[0].size(); l++) {
      |                                     ~~^~~~~~~~~~~~~

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