Raising an index on an (n, m) -tensor produces an (n + 1, m − 1) -tensor; this corresponds to moving diagonally down and to the left on the table. Symmetrically, lowering an index corresponds to moving diagonally up and to the right on the table. Contraction of an upper with a lower index of an (n, m) -tensor produces an (n − 1, m − 1) -tensor; this corresponds to moving diagonally up and to the left on the table.