code: @SafeVarargs
      public static <T> EventStream<T> merge(EventStream<? extends T>... inputs) {
          return new EventStreamBase<T>() {
              @Override
              protected Subscription observeInputs() {
                  return Subscription.multi(i -> i.subscribe(this::emit), inputs);
              }
          };
      }
docs: Returns an event stream that emits all the events emitted from any of
  the {@code inputs}. The event type of the returned stream is the nearest
  common super-type of all the {@code inputs}.
  
  @see EventStream#or(EventStream)