>> (defun hash-keys (hashtable)
It would have to be "hash-table-keys".
But again, I'm not sure it provides a useful enough abstraction to
justify adding this one-liner in every Emacs executable.
Tho, maybe we could introduce a new file "oneliners.el" where we could
collect such functions (probably most/all defined as `defsubst' so that
you can (eval-when-compile (require 'oneliners)).
Stefan