public static IObservable<PageSizeState> ObservePageSizeNotEqual(this PageManager pageManager, PageSizeState sizeState)
		{
			return pageManager.ObserveProperty(x => x.SizeState)
				.Where(x => x != sizeState);
		}
		public static IObservable<PageSizeState> ObservePageSizeGreaterThan(this PageManager pageManager, PageSizeState sizeState)
		{
			return pageManager.ObserveProperty(x => x.SizeState)
				.Where(x => x >= sizeState);
		}