anchor.diff:  let LensChoice() = checkLens "choice" (Car.make .|. Car.model)
   
   [<Test>]
  -let LensProduct() = checkLens "product" (Car.make *** Car.model)+let LensProduct() = checkLens "product" (Car.make *** Car.model)
  
positive.code: let stateMonadOperators() =
      let modify = 
          State.state {
              do! Employee.salary =! 1000
              do! Employee.salary += 100
          }
      let tom1 = modify tom |> snd
      Assert.AreEqual(1100, tom1.Salary)
  
negative.code: type Car = {
      Make: string
      Model: string
      Mileage: int
  } with 
      static member make = 
          { Lens.Get = fun (x: Car) -> x.Make
  