Returns the index of e in the given arr, or -1 if e is not found.

Returns the logical result of applying the given pred function to the arithmetic difference between every pair of elements in coll. When called without a predicate, returns true if all elements are in ascending sequence (ignoring duplicates).

This function is meant to be wrapped, e.g.,

(defn descending? [c] (ordered? neg? c))
(descending? [2 -1 -6 -8 -10 -13 -17])
;; => true