src/main/java/io/reactivex/Completable.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Completable ambWith(CompletableSource other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return ambArray(this, other);
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Completable ambWith(CompletableSource other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return ambArray(this, other);
    }
Returns a Completable that emits the a terminated event of either this Completable
or the other Completable whichever fires first.
<p>
<img width="640" height="484" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.ambWith.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code ambWith} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param other the other Completable, not null. A subscription to this provided source will occur after subscribing
to the current source.
@return the new Completable instance
@throws NullPointerException if other is null