Cancel command with Visual Lisp reactor

Hello

It is possible to cancel a command using visual lisp reactors, if someone has a possible example. If this is not there another way I could do that. I tried to use UNDEFINE but it works only with own CAD ​​commands and not with Visual Lisp command.

thank you

Under what ciircumstances you want to cancel a command?

UNDEFINE does not so much cancel a command as it does make the command unavailable. I wouldn't recommend its use unless there is a real good reason to undefine a particular command.