** Nested Tree Recursion: fringe**

Collect a list of the atoms on the fringe of a tree:

(define (fringe tree) (nreverse (fringeb tree '())))(define (fringeb tree lst) (if (pair? tree) (fringeb (cdr tree) (fringeb (car tree) lst)) (if (null? tree) lst (cons tree lst) ) ) )

> (fringe '(and (now) (for something (completely different)))) (and now for something completely different)

Note that since ` fringeb` uses ` cons` to build its answer,
the answer comes out backwards; therefore, ` fringe` uses
` nreverse` to reverse it.