anchor.diff:  namespace FSharp.RDF
   
   open VDS.RDF
  -open VDS.RDF.Writin 
  +open VDS.RDF.Writing
   open VDS.RDF.Parsing
   
   [<AutoOpen>]
  
positive.code:   let (|HasType|_|) t (R(_, xs)) =
      xs
      |> Seq.filter
           (fun ((P(Uri p)), (O(Uri o))) ->
           p = Uri.from (prefixes.rdf + "type") && t = o)
      |> Seq.map (fun (_, (O(Uri t))) -> t)
      |> Seq.toList
  
negative.code:     | _ -> false
  
  type Subject =
    | S of Uri
    static member from c = S(Uri.Curie c)
    static member from (u : string) = S(Uri.from u)
  
  type Predicate =
    | P of Uri
    static member from c = P(Uri.Curie c)
    static member from u = P(Uri.Sys u)
    static member from u = P(Uri.Sys(System.Uri u))
  
  type Object =
    | O of Node
  