anchor.diff:            Traversal of TraversalError<Error>
   
   
  -module Pretty = 
  +module Pretty =
       open Starling.Core.Pretty
       open Starling.Core.Var.Pretty
       open Starling.Core.Command.Pretty
  
positive.code:                  <+> String why)
          | Traversal err -> printTraversalError printError err
  
  
      /// Print infix operator across multiple lines
      let infexprV (op : string) (pxs : 'x -> Doc) (xs : seq<'x>) : Doc = 
          let mapped = Seq.map pxs xs 
          let resseq = Seq.map (fun x -> vsep [(String op); Indent x]) (Seq.tail mapped) 
          parened (hsep [Seq.head mapped; (hsep resseq)]) 
  
      /// Print infix operator on one line
      let infexpr (op : string) (pxs : 'x -> Doc) (xs : seq<'x>) : Doc = 
          let mapped = Seq.map pxs xs 
          let resseq = Seq.map (fun x -> hsep [(String op); x]) (Seq.tail mapped) 
          parened (hsep [Seq.head mapped; (hsep resseq)]) 
  
      /// Prints a marked Var 
      let printMarkedVarGrass (v : MarkedVar) : Doc =
          match v with 
          | Before s -> String "before_" <-> String s 
          | After s -> String "after_" <-> String s
          | Intermediate (i, s) -> String "inter_" <-> String (sprintf "%A_" i) <-> String s 
          | Goal (i, s) -> String "goal_" <-> String (sprintf "%A_" i) <-> String s 
  
      /// <summary>
      ///     Prints a shadow variable.
  
negative.code: ///     This model contains procedures for each term in the existing model,
  ///     as well as procedures for deferred checks.
  /// </summary>
  let grassModel (model : Backends.Z3.Types.ZModel) : Result<GrassModel,Error> =
      let fails = extractFailures model
      let failSeq = Map.toSeq fails
  
  