I attach a patch for the function bibtex-reformat in
lisp/textmodes/bibtex.el to avail of the function and flexibility of
map-y-or-n-p instead of emulating it.

If bug reports are not the preferable channel for such minor
suggestions, please let me know what to do in the future.

Thanks,

-- 
Basil

In GNU Emacs 27.0.50 (build 13, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2018-01-03 built on thunk
Repository revision: f8b4e87d5d4f57954b50677add76ce5136211dc1
Windowing system distributor 'The X.Org Foundation', version 11.0.11905000
System Description: Debian GNU/Linux testing (buster)