Several times already I've tried to write about a function that is "defined" or "undefined" somewhere using LaTex, but I get the following error message: [LaTex Error: Restricted command found (def)]
Since I can't believe we can't write "defined" using LaTex. what is the way to overcome these restrictions? I tried using " ", enclosing the word in brackets  , etc., but nothing.
Thanx for reading