Write an emacs/lisp program (Provide proof it works)

Implement a function in Lisp that takes in one parameter that is a list and returns the previous to last element of the list. If the list has less than two elements, it should return nil. Use the while loop for this.

Examples of results: (previous t '()) ; nil (previous '(a)) ; nil (previous '(12 83) ) ; 12 (previous '(a b c d e)) ; 'd