anchor.diff:  
   [<AutoOpen>] 
   module Types =
  -    type GrassModel = Backends.Z3.Types.ZModel // Just piggyback on Z3 model for now.  
  -    type Error = unit 
  +    type GrassModel = Backends.Z3.Types.ZModel  // Just piggyback on Z3 model.  
  +    type Error = unit                           // No Grasshopper-specific errors yet. 
   
   module Pretty = 
       open Starling.Core.Pretty
  
positive.code:         | Int name -> String name  
          | Bool name -> String name  
          | _ -> failwith "Unimplemented for Grasshopper backend." 
  
      // 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) 
          hsep [Seq.head mapped; (hsep resseq)] 
          |> parened 
  
      // 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) 
          hsep [Seq.head mapped; (hsep resseq)] 
          |> parened 
  
      /// Pretty-prints an arithmetic expression.
      let rec printIntExprG (pVar : 'Var -> Doc) : IntExpr<'Var> -> Doc =
  
negative.code:                     |> Indent |> braced 
               ]  
  
      /// Print all the Grasshopper queries for a model.      
      let printQuery (model: GrassModel) : Doc = 
          Map.toSeq model.Axioms 
          |> Seq.map (fun (name,term) -> printZTermGrass model.SharedVars name term) 
          |> vsep
  
      /// Print a Grasshopper error. 
      let printGrassError e = failwith "not implemented yet" 
  
  /// Generate a grasshopper model (currently doesn't do anything) 
  let grassModel (i : Backends.Z3.Types.ZModel) : Result<GrassModel,Error>  = 
    ok i 
  