rev-map function

Given an indicator function (A->B) and a list of items of A, return
an association list associating B to the elements that map to it;
essentially the inverse map of the indicator.

packages.lisp

@@ -29,7 +29,8 @@
   (:use :cl :lib.macros)
   (:export
    :parse-integer*
-   :range :take :split))
+   :range :take :split
+   :rev-map))
 
 (defpackage main
   (:use :cl :lib.macros)