anchor.diff:  
       [<Fact>]
       let ``a property should correctly return the stored value`` () =
  -        let p = new ObservableProperty<_>(0)
  +        let p = oref 0
   
           p <~ 5
           Assert.True(!!p = 5)
  
positive.code: 
      [<Fact>]
      let ``property behavior should only yield value changes`` () =
          let p = new ObservableProperty<_>(0)
          p <~ 5
  
          let o = record p.Behavior
  
negative.code: 
      [<Fact>]
      let ``property changes should be observed correctly`` () =
          let p = oref 0
          let vs = record (p :> IReadableProperty<_>).WhenValueSet
  
          p <~ 1
  