;; *** before: ***
(update-in {:count 1} [:count] inc)
;=> {:count 2}
(update-in {:count 1} [:count] + 5)
;=> {:count 6}

;; *** in version 1.7: ***
;; update does the same thing for a single top-level key,
;; without wrapping it into a one-element path vector
(update {:count 1} :count inc)
;=> {:count 2}
(update {:count 1} :count + 5)
;=> {:count 6}