;L3P9
;Write a function that removes all occurrences of an atom from any level of a list.
;removeEl(l a)
;   l - list of elements
;   a - given atom that will be removed from l
;removeEl(l, a)={
;   nil, if l is null
;   l, if l == a
;   nil, if l != a
;   append of lists returned by the mapcar call of a
;       lambda(I used a lambda function because removeEl has 2 parameters) function on l, otherwise
;}
(defun removeEl(l a)
  (cond
    ((null l) nil)
    ((and (atom l) (not (equal l a))) (list l))
    ((atom l) nil)
    (T (apply #'append (mapcar (lambda (ll) (removeEl ll a)) l)))
    )
  )
(write(removeEl (list 1 2 3 (list 4 1 (list 5 1)) 6 1) 1))