anchor.diff:      let main () =
           printfn "version 1"
   
  +        (importDefault<obj> "jcanvas") $ (jq, Browser.window) |> ignore
  +
           let w, h = WORLD_WIDTH, WORLD_WIDTH
           let mazeWidth = w*ROOM_SIZE + (w + 1)*DOOR_SIZE 
           let mazeHeight = h*ROOM_SIZE + (h + 1)*DOOR_SIZE
  
positive.code:         let button = jq $ ("#restart")  
  
          canvas ? width(mazeWidth) ? height(mazeHeight) |> ignore
          button ? click(fun _ ->
              cancel ()
              cancel <- startAnimation canvas
  
negative.code:     let [<Literal>] DOOR_SIZE = 5
  
      let jq = importDefault<obj> "jquery"
  
      // let renderBox className (x: int) (y: int) (w: int) (h: int) =
      //     sprintf "M%d,%d h%dv%dh%dz" x y w h -w
  