/in/foo.cc:37:5: error: 'Vector3' does not name a type; did you mean 'Vector2'?
   37 |     Vector3 operator*(const int k)
      |     ^~~~~~~
      |     Vector2
/in/foo.cc:42:5: error: 'Vector3' does not name a type; did you mean 'Vector2'?
   42 |     Vector3 operator+(const Vector2& v)
      |     ^~~~~~~
      |     Vector2
/in/foo.cc:46:5: error: 'Vector3' does not name a type; did you mean 'Vector2'?
   46 |     Vector3 operator-(const Vector2& v)
      |     ^~~~~~~
      |     Vector2
/in/foo.cc: In member function 'Matrix3 Matrix3::operator*(const Matrix3&)':
/in/foo.cc:131:13: warning: unused variable 'matrix' [-Wunused-variable]
  131 |         int matrix[9];
      |             ^~~~~~