i cannot understand about this consumer theory's theorem..can you please explain with a simple explanation? THEOREM 1.5 Differentiable Demand Let x* >> 0 solve the consumer's maximisation problem at prices p >> 0 and income yo > 0. If . u is twice continuously differentiable on R4, . du(x*) /axi > 0 for some i = 1, . .., n, and . the bordered Hessian of u has a non-zero determinant at x*, then x(p, y) is differentiable at (po, yo)