code: @SafeVarargs
  	public static <I> Flux<I> first(Publisher<? extends I>... sources) {
  		return onAssembly(new FluxFirstEmitting<>(sources));
  	}
docs: Pick the first {@link Publisher} to emit any signal (onNext/onError/onComplete) and
  replay all signals from that {@link Publisher}, effectively behaving like the
  fastest of these competing sources.
  
  <p>
  <img class="marble" src="doc-files/marbles/firstForFlux.svg" alt="">
  
  @param sources The competing source publishers
  @param <I> The type of values in both source and output sequences
  
  @return a new {@link Flux} behaving like the fastest of its sources