(.using
 [library
  [lux "*"
   [abstract
    [equivalence {"+" Equivalence}]
    [hash {"+" Hash}]]
   [data
    ["[0]" product]
    [text
     ["%" format]]
    [collection
     ["[0]" set {"+" Set}]]]
   [math
    [number
     ["[0]" nat]]]]]
 [//
  ["[0]" module]
  ["[0]" artifact]])

(type: .public ID
  (Record
   [#module module.ID
    #artifact artifact.ID]))

(def: .public hash
  (Hash ID)
  (all product.hash
       nat.hash
       nat.hash))

(def: .public equivalence
  (Equivalence ID)
  (# ..hash equivalence))

(def: .public none
  (Set ID)
  (set.empty ..hash))

(def: .public (format it)
  (%.Format ID)
  (%.format (%.nat (the #module it))
            "."
            (%.nat (the #artifact it))))