So, in Lispy languages you can access the head and tail of a list with `car` and `cdr` (insert historical sidebar here about what these names originally meant). But maybe you want the second element of a list -- that is, the head of the tail of the list. Or maybe the list's elements are themselves lists and you want the tail of the head. And so on. For this reason, there are pair accessor shorthands: (caar ls) is shorthand for (car (car ls)), (cdar ls) is shorthand for (cdr (car ls)), and so on.