Additional assumption for hwk 8- (3-3)

Please note that in (3-3), x_h^i denote the demand of good h for consumer i.
There may be several ways to solve this problem.
If you need to assume u_{12}^2, u_{21}^2>0, please do so.
(where u_{12}^2 =\frac{\partial^2 u^2 (x_1^2,x_2^2;a)}{\partial x_1^2 \partial x_2^2}.)

Nakajima