anchor.diff:  
               let r = System.Random()
               let isActives = Array.init n (fun _ -> Mod.init (r.NextDouble() > 0.5))
  -            let sphere = Sphere.solidSphere C4b.Red 1
  +            let sphere = Sg.sphere' 2 C4b.Red 1.0
               let objects = 
                   [| for i in 1 .. n - 1 do 
                       let sg = Sg.onOff isActives.[i] sphere
  
positive.code:         let cameraView  = Mod.constant initialView
  
          let candidates = 
              [| for _ in 1 .. 9 do yield Helpers.box C4b.Red Box3d.Unit |> Sg.ofIndexedGeometry |]
  
          let scale = 100.0
          let rnd = Random()
  
negative.code:         let cameraView  = DefaultCameraController.control win.Mouse win.Keyboard win.Time initialView
  
          let candidates = 
              [| for _ in 0 .. 8 do yield Sg.box' C4b.Red Box3d.Unit  |]
  
          let scale = 100.0
          let rnd = Random()
  