anchor.diff:              [
                   "on" => (ForceEvent?``type`` ^-> (O ^-> O)) + chained (ForceEvent?``type`` * (O ^-> O)?listener)
                   "nodes" => getSetVal chained !|ForceNode
  -                "links" => getSetVal chained !|(Link ForceNode)
  +                "links" => getSetVal chained !|Link.[ForceNode]
                   "start" => chained O
                   "alpha" => getSetVal chained Float
                   "resume" => O ^-> O
  
positive.code:         let self = Type.New()
          Class "Set"
          |=> self
          |+> Protocol [
              "has"     => String?value ^-> Bool
              "add"     => String?value ^-> String
              "remove"  => String?value ^-> Bool
  
negative.code:         ChainedClass "Treemap" self <| fun chained ->
              [
                  "nodes"     => PartitionNode?root ^-> !|PartitionNode
                  "links"     => (!|PartitionNode)?nodes ^-> !|Link.[PartitionNode]
                  "children"  => getSetVal chained (Obj ^-> Obj)
                  "sort"      => getSetVal chained Comparator
                  "value"     => getSetVal chained (Obj ^-> Float)
  