title: 如何建立一个从N到{∅，{∅}，{{∅}}，{{{∅}}}...}的双射？
desc: 显然是存在双射的，但能否用严格的数学语言将它表示出来？
topic: 数学
content: Method1 let S，，，，，，...， N set of natural numbers f N-->S let f0，f1， f2， fnfn-1fn-1fn-2 for all n larger than or equals to 3 fn have n elements inside It is obvious that it is injective and surjective， hence bijective. Method2 Let g N-->，，... g0， gngn-1， it is easy to
answerer_tags: 好想要宅的小伙伴 ฅ( ̳• ·̫ • ̳ฅ)/现在偶尔冒个泡