フィボナッチ数列
https://blog.miz-ar.info/2019/01/fast-fibonacci/
https://qiita.com/mod_poppo/items/4f78d135bb43b7fd1743
遅延評価
を活かす
https://omochist.hatenadiary.org/entry/20060531/1149060300
https://lethevert.hatenadiary.org/entry/20060531/p5
https://www.math3ma.com/blog/fibonacci-sequence
フィボナッチ数列は
関手