code: public static <T, U, R> ToDoubleBiFunction<T, U> compose(
          final ToDoubleBiFunction<? super T, ? super U> biFunction, 
          final DoubleUnaryOperator operator)
      {
          return (x,y) -> operator.applyAsDouble(biFunction.applyAsDouble(x, y));
      }
docs: Composes the given functions
  
  @param <T> The first argument type
  @param <U> The second argument type
  @param <R> The first result type
  
  @param biFunction The {@link ToDoubleBiFunction}
  @param operator The {@link DoubleUnaryOperator}
  @return The resulting {@link ToDoubleBiFunction}