anchor.diff:  open System.Reactive.Subjects
   open System.Reactive.Linq
   
  +/// A read-only property variable.
   type IReadableProperty<'a> =
       /// Current value of the property
       abstract Value : 'a
       /// An observable that generates a value when this IReadableProperty<'a> is being set.
       abstract WhenValueSet : IObservable<'a>
   
  +/// A write-only property variable.
   type IWriteableProperty<'a> =
       /// Set the current value of the property
       abstract Set : 'a -> unit
  
positive.code:             ObservableProperty.sync property convert counterpart convertBack
  
      type IObservable<'a> with
          member observable.AsProperty (initialValue) =
              new ObservablePropertyFromObservable<'a>(observable, initialValue)
  
      type IObserver<'a> with
          member observer.AsProperty () =
              { new IWriteableProperty<'a> with
                  member this.Set(x) = observer.OnNext(x)
  
negative.code:         new CompositeDisposable(bind a mapTo b, bind b mapFrom a) :> _
  
  module Operators =
      /// Creates a new ObservableProperty with a given initial value.
      let inline newP v = new ObservableProperty<_>(v)
  
      /// Assigns a new value to an IWriteableProperty.
      let inline (<~) (p : IWriteableProperty<'a>) (x : 'a) = p.Set(x)
  
      /// Gets current value of an IReadableProperty.
      let inline (!!) (p : IReadableProperty<'a>) : 'a = p.Value
  
      /// 'Binds' an IReadableProperty (left operand) to an IWriteableProperty (right operand),
      /// projecting the values with given map function.
      let inline ( @~> ) (from', mapTo) to' = ObservableProperty.bind from' mapTo to'
  
      /// 'Binds' an IReadableProperty (left operand) to an IWriteableProperty (right operand),
      /// projecting the values with given map function.
      let inline ( <~@ ) to' (from', mapTo) = ObservableProperty.bind from' mapTo to'
  
      let inline (<~@~>) (a, mapTo) (b, mapFrom) = ObservableProperty.sync a mapTo b mapFrom
  
  [<AutoOpen>]
  