The basic function that constructs new list structure is the function CONS.
If Y is a list, then we can think of (CONS X Y) as adding the new element X to the front of the list Y.
(CONS 'A '(B)) = (A B) (CONS 'A NIL) = (A) (CONS 'A '()) = (A) (CONS '(A) '(B)) = ((A) B) (CONS 'A 'B) = (A . B)
The following axioms always hold: