For any tensor field N μ μ ν ν . . . , we may call N μ μ ν ν . . . − − g a tensor density, where g is the determinant of the metric tensor g μ μ ν ν . The integral ∫ ∫ N μ μ ν ν . . . − − g d 4 x is a tensor if the domain of integration is small. It is not a tensor if the domain of integration is not small, because it then consists of a sum of tensors located at different points and it does not transform in any simple way under a transformation of coordinates. Here we consider only small domains. This is also true for the integration over the three-dimensional hypersurface S ν ν .