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
(command "abc" "")
These two separate statements are not usable. Looking for something different.
(if(= command "abc" nil)(alert "Not Found"))
(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).
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