foo.cc: In function 'int main()':
foo.cc:131:37: error: cannot bind non-const lvalue reference of type 'Matrix&' to an rvalue of type 'Matrix'
  131 |  Matrix ans1 = (mat1 + mat2 - mat3) * k;
      |                ~~~~~~~~~~~~~~~~~~~~~^~~
foo.cc:13:17: note:   initializing argument 1 of 'Matrix::Matrix(Matrix&)'
   13 |  Matrix(Matrix& obj)
      |         ~~~~~~~~^~~
foo.cc:132:37: error: cannot bind non-const lvalue reference of type 'Matrix&' to an rvalue of type 'Matrix'
  132 |  Matrix ans2 = (mat1 * mat2 * mat3) * k;
      |                ~~~~~~~~~~~~~~~~~~~~~^~~
foo.cc:13:17: note:   initializing argument 1 of 'Matrix::Matrix(Matrix&)'
   13 |  Matrix(Matrix& obj)
      |         ~~~~~~~~^~~

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