anchor.diff:      let giveRaise = Editor.salary += 1000
       let tom1 = { tom with Salary = tom.Salary + 1000 }
       let tom2 = tom |> Editor.salary += 1000
  +    let tom3 = giveRaise tom
       Assert.AreEqual(tom1, tom2)
  +    Assert.AreEqual(tom1, tom3)
   
   [<Test>]
   let setValueOperator() =
  
positive.code:         }
      let tom1 = modify tom |> snd
      Assert.AreEqual(1100, tom1.Salary)
  
  type LensProperties =
      /// If the view does not change, neither should the source.
  
negative.code: 
  [<Test>]
  let update() =
      let tom1 = { tom with Salary = tom.Salary + 1000 }
      let tom2 = tom |> Lens.update ((+) 1000) Editor.salary
      let tom3 = tom |> Editor.salary.Update ((+) 1000)
  