@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Observable<R> scanWith(Callable<R> seedSupplier, BiFunction<R, ? super T, R> accumulator) {
        ObjectHelper.requireNonNull(seedSupplier, "seedSupplier is null");
        ObjectHelper.requireNonNull(accumulator, "accumulator is null");
        return RxJavaPlugins.onAssembly(new ObservableScanSeed<T, R>(this, seedSupplier, accumulator));
    }