anchor.diff:          type Polygons = pset<Polygon>
   
           type Scene = { polygons : Polygons }
  +
           type State = { polygon : pmod<list<V3f>>; unique : Scope.Unique; 
                          hoverPosition : IModRef<Option<Polygon * pmod<V3f>>>; 
                          selectedPoint : ref<Option<pmod<V3f>>>
  
positive.code: 
              win.Mouse.Click.Values.Subscribe(fun c ->
                  match c with 
                   | MouseButtons.Left  -> interactGit (camPick |> Mod.force |> Option.map V3f.op_Explicit |> Option.get |> AddPoint) 
                   | MouseButtons.Right -> interactGit ClosePolygon 
                   | MouseButtons.Middle -> interactGit <| ToggleMoving
                   | _ -> ()
              ) |> ignore
  
  
negative.code:                                 |> Seq.toList
                          match nearbyRay with
                              | [] -> ()
                              | (p,bestPosition,d) :: _ when d < Double.MaxValue && not !state.dragging -> 
                                  yield fun () -> 
                                      Mod.change state.hoverPosition (Some (p, bestPosition)) 
                              | _ -> 
  