anchor.diff:  namespace FSharp.RDF
   
   open VDS.RDF
  -open VDS.RDF.Writin 
  +open VDS.RDF.Writing
   open VDS.RDF.Parsing
   
   [<AutoOpen>]
  
positive.code:     | _ -> false
  
  type Subject =
    | S of Node
    static member from c = S(Node.Uri(Uri.Curie c))
    static member from (u : string) = S(Node.from u)
  
  type Predicate =
    | P of Node
    static member from c = P(Node.Uri(Uri.Curie c))
    static member from u = P(Node.Uri(Uri.Sys u))
    static member from u = P(Node.Uri(Uri.Sys(System.Uri u)))
  
  type Object =
    | O of Node
  
negative.code:       for (p, o) in px -> (s, p, o)
      }
  
    let mapObject f (O o) = f o
  
    let mapO f = List.map (mapObject f)
  
    let id (R(S s,_)) = s
  
    let traverse xo =
      [ for o in xo do
          match o with
  