I cannot understand about this producer theory's theorem. Can you please explain with a simple explanation? THEOREM 3.3 Properties of Conditional Input Demands Suppose the production function satisfies Assumption 3.1 and that the associated cost function is twice continuously differentiable. Then 1. x(w, y) is homogeneous of degree zero in w, 2. The substitution matrix, defined and denoted ax1 (w, y) ax1 (w, y) aw1 own o* (w, y)= axn (W, y) AXn (W, y) aw1 awn is symmetric and negative semidefinite. In particular, the negative semidefiniteness property implies that axi(w, y) / awi