comparator
(comparator pred)
clojure.core/comparator: a two-argument function answering -1 when (pred a b) is
truthy, else 1 when (pred b a) is, else 0. It turns a predicate such as < or >
into the comparator sort, sort-by, sorted-map-by and sorted-set-by take. As a value
a one-argument function.