code: public final <R> ParallelFlux<R> reduce(Supplier<R> initialSupplier,
  			BiFunction<R, ? super T, R> reducer) {
  		Objects.requireNonNull(initialSupplier, "initialSupplier");
  		Objects.requireNonNull(reducer, "reducer");
  		return onAssembly(new ParallelReduceSeed<>(this, initialSupplier, reducer));
  	}
docs: Reduces all values within a 'rail' to a single value (with a possibly different
  type) via a reducer function that is initialized on each rail from an
  initialSupplier value.
  <p>
  Note that the same mapper function may be called from multiple threads
  concurrently.
  
  @param <R> the reduced output type
  @param initialSupplier the supplier for the initial value
  @param reducer the function to reduce a previous output of reduce (or the initial
  value supplied) with a current source value.
  
  @return the new {@link ParallelFlux} instance