foldl1 - mrsekut-p

foldl1

from foldl

http://www.ndis.co.jp/blog/tech/2009/03/fold-2.html

http://zvon.org/other/haskell/Outputprelude/foldl1_f.html

https://blog.miz-ar.info/2019/10/scanl-and-scanr/

https://xtech.nikkei.com/it/article/COLUMN/20091009/338681/?P=4