(.using
 [library
  [lux {"-" Type}
   [abstract
    [equivalence {"+" Equivalence}]
    [order {"+" Order}]
    [hash {"+" Hash}]]
   [data
    ["[0]" product]
    ["[0]" text ("[1]#[0]" order)
     ["%" format {"+" format}]]]]]
 ["[0]" // "_"
  ["[1]" artifact {"+" Artifact} ("[1]#[0]" order)
   [type {"+" Type}]]])

(type: .public Dependency
  (Record
   [#artifact Artifact
    #type Type]))

(def: .public hash
  (Hash Dependency)
  ($_ product.hash
      //.hash
      text.hash
      ))

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

(implementation: .public order
  (Order Dependency)

  (def: equivalence
    ..equivalence)

  (def: (< reference subject)
    (<| (or (//#< (the #artifact reference)
                  (the #artifact subject)))
        
        (and (//#= (the #artifact reference)
                   (the #artifact subject)))
        (text#< (the #type reference)
                (the #type subject)))))