src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> amb(Iterable<? extends ObservableSource<? extends T>> sources) {
        ObjectHelper.requireNonNull(sources, "sources is null");
        return RxJavaPlugins.onAssembly(new ObservableAmb<T>(null, sources));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> amb(Iterable<? extends ObservableSource<? extends T>> sources) {
        ObjectHelper.requireNonNull(sources, "sources is null");
        return RxJavaPlugins.onAssembly(new ObservableAmb<T>(null, sources));
    }
Mirrors the one ObservableSource in an Iterable of several ObservableSources that first either emits an item or sends
a termination notification.
<p>
<img width="640" height="385" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/amb.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code amb} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <T> the common element type
@param sources
an Iterable of ObservableSource sources competing to react first. A subscription to each source will
occur in the same order as in the Iterable.
@return an Observable that emits the same sequence as whichever of the source ObservableSources first
emitted an item or sent a termination notification
@see <a href="http://reactivex.io/documentation/operators/amb.html">ReactiveX operators documentation: Amb</a>