Consider the production possibilities set
Y = {(y1; y2) : y2 小于等于(y1)的z次方 , z 属于 Z+},
where Z+ denotes the set of non-negative integers.
(a) For which values of z is Y valid in the sense of being technically reasonable?
Explain in terms of the possible graphs of Y .
(b) Show whether or not each valid Y is closed, convex, and satises free disposal.
(c) Characterize the set of efcient points of each valid Y .
(d) What returns to scale property does each valid Y exhibit, if any?

第一问的technically reasonable是不是指符合日常生产生活？那这样的话，Z=0，y1恒等于1，无论怎么投入y2都不增加，就不符合technically reasonable了吧？

还有第二问，应该怎么做？
第三问，当小于等于号变成等号的时候，就变成efficient points了吧？就是在线上？
第四问，当Z=1，规模报酬不变，Z大于1，规模报酬递增

请大家看看我的思路对不对，并且解决第二问，谢谢了