> t
(1 (2 () ()) (3 (4 () ()) (5 () ())))
> (depth t)
3
> (memv-tree 2 t)
(2 () ())
> (memv-tree 3 t)
(3 (4 () ()) (5 () ()))
> (or #t #f)
#t
> (or #f #f)
#f
> (or 12 #f)
12
> (or #f 23)
23
> (or x y) <-> (if x x y)
> (and #f 12)
#f
> (and 23 #f)
#f
> (and 23 45)
45
> (path-tree 1 t)
(1)
> (path-tree 2 t)
(1 2)
> (path-tree 3 t)
(1 2 . #f)
> (path-tree 3 t)
(1 3)
> (path-tree 4 t)
(1 3 4)
> (path-tree 5 t)
(1 3 5)
> (path-tree 5 t)
(1 3 5)
> (path-tree 6 t)
#f
> (search  (lambda (x) (path-tree x t) '(6 4 2)))
(1 3 4)
> (exists?  (lambda (x) (path-tree x t)) '(6 4 2))
#t