oh...it was a user (@LilyXY) who's either blocked me, or who disabled their profile, or something else (it's really hard for me to tell exactly), who recommended the book. all I have is my response in which I thanked Lily for the recommendation...but now I can't view the recommendation. blech.
let this be a lesson to me: if I'm supplied a tidbit of information through mastodon or Twitter, _save a copy immediately_