It looks like an error. The author probably based his code on an example from Wikibooks [1]: (def fib-seq (lazy-cat [0 1] (map + (rest fib-seq) fi

It looks like an error. The author probably based his code on an example from Wikibooks [1]: (def fib-seq (lazy-cat [0 1] (map + (rest fib-seq) fib-seq))) But, since he added an argument to the function, I don't think his code actually works, even if you ran :s/fib-seq/fibonacci [1]: https://en.wikibooks.org/wiki/Clojure_Programming/Examples/Lazy_Fibonacci https://en.wikibooks.org/wiki/Clojure_Programming/Examples/L...