Found on the Emacs Wiki https://www.emacswiki.org/emacs?action=browse;diff=1;id=CommonLispEmacs
See also https://lisperator.net/s/slip/ for an in-browser Lisp implementation.  The latter (SLip build fc7e29c 2025-10-21 20:08:55) does not compute (tan x) correctly, I reported this on 2025-10-30. SLip build d1c5dfe 2025-11-03 22:51:27 has working atan (with one argument only) and tan functions.
It is lacking apropos and describe, which would be very useful. https://jscl-project.github.io/ does have these functions.