According to Einstein notation, when an index variable appears twice in a single term and is not otherwise defined, it implies summation of that term over all the values of the index; also, the not all upper indices are not exponents but are indices of coordinates.
According to Einstein notation, when an index variable appears twice in a single term and is not otherwise defined, it implies summation of that term over all the values of the index; also, the not all upper indices are not exponents but are indices of coordinates.