The new patch has more sense to me.

I correct my previous wish about the func. behaviour with respect N:
*) N nil give same output as N = 1.
*) N <= 0 return nil.


(let ((ltest '(1 2 3 4 5 6)))
   (nfront ltest 0))
nil
(let ((ltest '(1 2 3 4 5 6)))
   (nfront ltest -1))
nil
(let ((ltest '(1 2 3 4 5 6)))
   (nfront ltest 3))
(1 2 3)
(let ((ltest '(1 2 3 4 5 6)))
   (nfront ltest))
(1)
(let ((ltest '(1 2 3 4 5 6)))
   (nfront ltest 100))
(1 2 3 4 5 6)