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 ``two-way binding should work`` () =
          let a = new ObservableProperty<_>(0)
          let b = new ObservableProperty<_>(0)
  
          do
              use binding = (a, id) <~@~> (b, id)
  
negative.code: 
      [<Fact>]
      let ``property behavior should yield the current value first`` () =
          let p = oref 0
          p <~ 5
  
          let o = record p.Behavior
  