2> (list-zipper '(a (b (c d))))
#<zip (a (b (c d)))>
3> (down #2)
#<zip a>
4> (right #3)
#<zip (b (c d))>
5> (down #4)
#<zip b>
6> (right #5)
#<zip (c d)>
7> (down #6)
#<zip c>
8> (right #7)
#<zip d>
9> (up (up (up #8)))
#<zip (a (b (c d)))>