anchor.diff:  open Starling.Core.Instantiate
   open Starling.Core.GuardedView
   open Starling.Core.Traversal
  +open Starling.Backends.Z3
   
   [<AutoOpen>] 
   module Types =
  
positive.code:         | Reg r -> pReg r
          | Sym { Sentence = ws; Args = xs } ->
              let pArg = printExprG (printSym pReg)
              parened
                  (printInterpolatedSymbolicSentence pArg ws xs)
  
      /// Get the set of accessed variables. 
      let findVarsGrass (zterm : Backends.Z3.Types.ZTerm) : seq<MarkedVar> = 
  
negative.code:         | _ -> failwith "[printIntExprG] Unimplemented for Grasshopper backend." 
  
      /// Pretty-prints a Boolean expression.
      and printBoolExprG (pVar : 'Var -> Doc) (b : BoolExpr<'Var>) : Doc =
          match b with 
          | BVar c -> pVar c
          | BAnd xs -> infexprV "&&" (printBoolExprG pVar) xs 
          | BOr xs -> infexprV "||" (printBoolExprG pVar) xs
          | BImplies (x, y) -> infexprV "==>" (printBoolExprG pVar)  [x; y]
          | BNot (BEq (x, y)) -> infexpr "!=" (printExprG pVar) [x; y]
          | BEq (x, y) -> infexpr "==" (printExprG pVar) [x; y]
          | BGt (x, y) -> infexpr ">" (printIntExprG pVar) [x; y]
          | BLt (x, y) -> infexpr "<" (printIntExprG pVar) [x; y]
          | _ -> failwith "[printBoolExprG] Unimplemented for Grasshopper backend."  
         
      /// Pretty-prints an expression.
      and printExprG (pVar : 'Var -> Doc) : Expr<'Var> -> Doc =
          function
  