let - What does this Scheme code do? -

especially why using tailr , headr? not able understand.

(define (foo lst)   (cond     ((not (list? lst)) lst)     ((null? lst) lst)     (else (let* ((tail (cdr lst))                  (head (car lst))                  (tailr (foo tail))                  (headr (foo head)))             (append tailr (list headr)))))) 

it equivalent to:

(define (reverse-nested lst)   (cond ((not (pair? lst)) lst)         (else (reverse (map reverse-nested lst)))))