gistfile1.clj

(let [valid? (fn [pos]
               (every? true?
                       ;; here we make use of extra-arity map <
                       ;; map "expands" like (and (< -1 y h)
                       ;;                         (< -1 x w))
                       ;; with 3+ args, < tests "ascending", so we can pin
                       ;; y and x in the range of [0, max).
                       (map < [-1 -1] pos dims)))