Command exist or not !!! How to find?? LISP

Hi,
i want to know if the command exist in the autocad or not. Actually i
am using separate software(H2ONET) that runs on autocad.
Let's say abc is a command and i want to know where the autocad can use
abc command or not....eg..

(command "abc" "")

These two separate statements are not usable. Looking for something
different.

(if(= command "abc" nil)(alert "Not Found"))

and

(atoms-family 0 '("abc")) or
(atoms-family 0 '("c:abc"))

Typing abc in the command line works but (atoms-faily 0'("abc")) gives
me (nil).