code: import java.util.Arrays;
  import java.util.Optional;
  import java.util.function.Function;
  import java.util.function.BiFunction;
  
  @FunctionalInterface
  public interface VarargsFunction<INPUTS, OUTPUT> extends Function<INPUTS[], OUTPUT> {
    @SuppressWarnings("unchecked")
    public OUTPUT apply(INPUTS... inputs);
  
    public static <INPUTS, OUTPUT> VarargsFunction<INPUTS, OUTPUT> from(Function<INPUTS[], OUTPUT> function) {
      return function::apply;
    }
  
    public static <INPUTS, OUTPUT> VarargsFunction<INPUTS, OUTPUT> upgrade(Function<INPUTS, OUTPUT> function) {
      return inputs -> function.apply(inputs[0]);
    }
  
    public static <INPUTS, OUTPUT> VarargsFunction<INPUTS, OUTPUT> upgrade(BiFunction<INPUTS, INPUTS, OUTPUT> function) {
      return inputs -> function.apply(inputs[0], inputs[1]);
    }
  
    @SuppressWarnings("unchecked")
    public default <POST_OUTPUT> VarargsFunction<INPUTS, POST_OUTPUT> andThen(
        VarargsFunction<OUTPUT, POST_OUTPUT> after) {
      return inputs -> after.apply(apply(inputs));
    }
  
    @SuppressWarnings("unchecked")
    public default Function<INPUTS, OUTPUT> toFunction() {
      return input -> apply(input);
    }
  
    @SuppressWarnings("unchecked")
    public default BiFunction<INPUTS, INPUTS, OUTPUT> toBiFunction() {
      return (input, input2) -> apply(input, input2);
    }
  
    @SuppressWarnings("unchecked")
    public default <PRE_INPUTS> VarargsFunction<PRE_INPUTS, OUTPUT> transformArguments(Function<PRE_INPUTS, INPUTS> transformer) {
      return inputs -> apply((INPUTS[]) Arrays.stream(inputs).parallel().map(transformer).toArray());
    }
  }
  