anchor.diff:      open Starling.Core.Axiom.Pretty
       open Starling.Core.View.Pretty
       open Starling.Core.GuardedView.Pretty
  +    open Starling.Core.Symbolic.Pretty
  +    open Starling.Core.Var.Pretty
   
   
       /// <summary>
  
positive.code: [<AutoOpen>]
  module Types =
      /// <summary>
      ///     A <see cref="ViewExpr"/> of the type permitted in a Graph.
      /// </summary>
      type GraphViewExpr = ViewExpr<IteratedGView<Sym<Var>>>
  
      /// <summary>
      ///     An edge identifier.
  
negative.code: ///     to <paramref name="nodeView" />.
  /// </returns>
  let nodeHasView
    (nodeName : NodeID) (nodeView : GraphView) (graph : Graph)
    : bool =
      match (Map.tryFind nodeName graph.Contents) with
      | Some (InnerView v, _, _, _) -> v = nodeView
  