anchor.diff:  namespace Infers.Toys
   
   module Zipper =
  -
  +  open System.Collections.Generic
  +  open System
     open Infers
     open Infers.Rep
   
  
positive.code:         member t.Set d = r := d}
  
      member z.Prim (_: Prim<'t>) = downNone<'w, 't>
      member z.Unsupported (_: Unsupported<'t>) =
        printfn "WARNING: Type %A may not be properly supported by Zipper." typeof<'t>
        downNone<'w, 't>
  
      member z.String () : Down<'w, string> =
  
negative.code:     abstract Un: byref<'v> * byref<'h> * byref<'n> * byref<'p> -> unit
  
    type [<InferenceRules>] Zipper () =
      static let warned = Dictionary<Type, unit> ()
  
      member z.ToZipper (_: Rep, wD: Down<'w, 'w>) =
        {new Up<'w, 'w> () with
          member u.Up w =
  