If you are running Project Euler problems, I don’t want to ruin the exercise for you, but here is how you define the Fibonacci sequence so that lazy-seq saves the “update” on its own:
(defn fib-maker
([] (concat [0 1] (fib 0 1)))
([a b] (lazy-seq (cons b (fib b (+ a b))))))
(def fib (fib-maker))
, , , , . , , , .