Exercise 2.17.  Define a procedure last-pair that returns the list that 
contains only the last element of a given (nonempty) list:

(last-pair (list 23 72 149 34))
(34)

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(define (last-pair items)
  (if (null? (cdr items))
      (car items)
      (last-pair (cdr items))))

That is incorrect, a correct solution returns a list, not the item, 
e.g. (cons (car items) nil).