Since combinations of car and cdr are frequently used, all combinations up to four uses of car and cdr are defined as functions of the form cxxxr:
(caar x) = (car (car x))(cadr x) = (car (cdr x))
(caddr x) = (car (cdr (cdr x)))
Rule: The operations closer to the argument are done first.
It's worth memorizing some common combinations:
| car | = | first element of a list |
|
cadr | = | second element |
|
caddr | = | third element |
|
cadddr | = | fourth element |