solution on exercise 22 does not work on 1.6

The solution to exercise 22 seems to be :

(defn old-book->new-book [book](let [authors %28get book :authors%29]
%28assoc book :authors %28set authors%29%29))

but when you do this in 1.6.0 this is the output :

{:title "Wild Seed", :authors #{{:death-year 2006, :name "Octavia E. Butler", :birth-year 1947}}}

Is it a idea to update this course to the newer version.

Roelof