         before.start()
     }
 
-    func _startPresent(context: UIViewControllerContextTransitioning) {
+    private func _startPresent(context: UIViewControllerContextTransitioning) {
         let frame = context.finalFrameForViewController(context.viewControllerForKey(UITransitionContextToViewControllerKey)!)
         let fromView = context.viewForKey(UITransitionContextFromViewKey)!
         let toView = context.viewForKey(UITransitionContextToViewKey)!


    var duration: NSTimeInterval {

        var duration = 0.0
        for task: Task in tasks {
            var d: NSTimeInterval = {
                if let animation = task.animation {
                    return task.delay + animation.duration
                }

        return before.duration + present.duration
    }

    let before = Animator()
    let present = Animator()

    init(operation: UINavigationControllerOperation)  {
        self.operation = operation
