en_tn/2ki/15/21.md

are they not written ... Israel?

This question is used to either inform or remind the readers that the information about Menahem is in this other book. See how you translated this in 2 Kings 1:18. AT: "they are written in The Book of the Events of the Kings of Israel." (See: rc://en/ta/man/translate/figs-rquestion)