clisp の cadadr ってなんだ？

「Land of Lisp」という本を買った。3章の最後にあっさり出てくる cadadr は car と cdr の組み合わせだというのは解るのだが、どのように組み合わされたものなのか解読に苦労してしまった。c*r の * の a は car の略称、d は cdr の略称なのは想像がついたのだが・・・　そこで少しググってみて納得がいきました。頭悪いなと実感！

 (defun caar (x) (car (car x)))
 (defun cadr (x) (car (cdr x)))
 (defun cdar (x) (cdr (car x)))
 (defun cddr (x) (cdr (cdr x)))
 (defun caaar (x) (car (car (car x))))
 (defun caadr (x) (car (car (cdr x))))
 (defun cadar (x) (car (cdr (car x))))
 (defun caddr (x) (car (cdr (cdr x))))
 (defun cdaar (x) (cdr (car (car x))))
 (defun cdadr (x) (cdr (car (cdr x))))
 (defun cddar (x) (cdr (cdr (car x))))
 (defun cdddr (x) (cdr (cdr (cdr x))))
 (defun caaaar (x) (car (car (car (car x)))))
 (defun caaadr (x) (car (car (car (cdr x)))))
 (defun caadar (x) (car (car (cdr (car x)))))
 (defun caaddr (x) (car (car (cdr (cdr x)))))
 (defun cadaar (x) (car (cdr (car (car x)))))
 (defun cadadr (x) (car (cdr (car (cdr x)))))
 (defun caddar (x) (car (cdr (cdr (car x)))))
 (defun cadddr (x) (car (cdr (cdr (cdr x)))))
 (defun cdaaar (x) (cdr (car (car (car x)))))
 (defun cdaadr (x) (cdr (car (car (cdr x)))))
 (defun cdadar (x) (cdr (car (cdr (car x)))))
 (defun cdaddr (x) (cdr (car (cdr (cdr x)))))
 (defun cddaar (x) (cdr (cdr (car (car x)))))
 (defun cddadr (x) (cdr (cdr (car (cdr x)))))
 (defun cdddar (x) (cdr (cdr (cdr (car x)))))
 (defun cddddr (x) (cdr (cdr (cdr (cdr x)))))