I am having a problem that is glossed over in many text books but is driving me nuts. Consider the following inner product or one-form with a vector argument: dx_i(partial_j) = kroenicker delta ij Here, dx_i is a one-form and partial_j (the partial wrt x_j) is a vector. Some books say: dx_i(partial_j) = partial x_i / partial x_j = kroenicker delta ij The problem is that I can't see how this is true. (Well, I do know that partial x_i / partial x_j = kroenicker delta ij but I can't see the rest.) What am I missing here? Thanks.