where formula_15 is the Kronecker delta, which functions similarly to the identity matrix, and has the effect of renaming indices ("j" into "k" in this example). This shows several features of the component notation: the ability to re-arrange terms at will (commutativity), the need to use different indices when working with multiple objects in the same expression, the ability to rename indices, and the manner in which contravariant and covariant tensors combine so that all instances of the transformation matrix and its inverse cancel, so that expressions like formula_16 can immediately be seen to be geometrically identical in all coordinate systems.