Assuming that compensated demand x"(p, u) is unique (hence a function) and differentiable, show that: Vpx" (p, u) . p = 0 for i = 1, ..., n. or equivalently, in matrix notation: Dpx" (p, u) p = 0. Recalling the definition from class, conclude that every good in the system has at least one substitute. Hint: What is true about compensated demand x"(ap, u) as a function of o