Scheme explanation - cdr and car -

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i've got example : 

(apply + 2 (cdadr '(1 ((2 . 3) 4))))

this returns 6? why (cdadr '(1 ((2 . 3) 4))) 4?? don't it.shouldn't 3?

the result list '(4), not number 4.

you have list 2 elements, 1 first element, , list ((2 . 3) 4) second element.

in other words, cdr of list (cons ((2 . 3) 4)) '()), or (((2 . 3) 4)). 

> (cdr '(1 ((2 . 3) 4))) '(((2 . 3) 4))

this list 1 element - list ((2 . 3) 4) - of course car.

> (car (cdr '(1 ((2 . 3) 4)))) '((2 . 3) 4)

and, finally,

> (cdr (car (cdr '(1 ((2 . 3) 4))))) '(4)

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