anchor.diff:          | Bool b -> printBoolExpr pVar b
           | _ -> failwith "Unimplemented for Grasshopper backend." 
   
  +    /// Pretty-prints a symbolic sentence 
       let rec printSym (pReg : 'Reg -> Doc) (sym : Sym<'Reg>) : Doc =
           match sym with
           | Reg r -> pReg r
  
positive.code:         printBoolExpr (printSym printMarkedVar) a 
  
      let findVarsGrass (zterm : Backends.Z3.Types.ZTerm) : seq<MarkedVar> = 
          BAnd [zterm.SymBool.WPre; zterm.SymBool.Goal] 
          |> findMarkedVars (tliftToBoolSrc (tliftToExprDest collectSymMarkedVars)) 
          |> lift (Set.map valueOf) 
  
negative.code:                headed "Command" (cmdprint |> Seq.singleton)
               ]  
  
      let printGrassError e = 
          failwith "not implemented yet" 
  
  