7.10 (Rader, 1968) In the text we showed that the cross comparative statics terms x/w; for i j could not be signed for an n-input perfectly competitive firm when the only assumptions on the model were the first- and second-order conditions for profit maximization. Prove that if all inputs were "normal," that is, fij 0 for all i #j, then the factor inputs will never be gross substitutes (i.e., it will be the case that x*/w; 0 for all i j)