anchor.diff:          { /// <summary>
             ///      The name of the edge.
             /// </summary>
  -          Name : string
  +          Name : EdgeID
             /// <summary>
             ///      The destination of this edge.
             /// </summary>
  -          Dest : string
  +          Dest : NodeID
             /// <summary>
             ///      The command this edge represents.
             /// </summary>
  
positive.code:     ///     A pretty-printer <c>Command</c> that prints
      ///     <paramref name="graph" />.
      /// </returns>
      let printGraph graph =
          hsep [ String "digraph"
                 String graph.Name
  
  
                 // TODO(CaptainHayashi): don't convert here?
                 graph |> toSubgraph |> printSubgraph ]
  
negative.code: ///     If the edges are valid (reference indices in <paramref
  ///     name="nodes" />), then the result will be <c>ok</c>.
  /// </returns>
  let graph (name : string) (sg : Subgraph) : Result<Graph, Error> =
      // Are any of the node indices out of bounds?
      match (Map.filter
                 (fun _ {Pre = s; Post = t} ->
  