/**
 * This function takes a list of books and adds them to a shelf.
 * The function uses the plus assignment operator to add the books to the shelf.
 *
 * @param books A list of books to be added to the shelf.
 * @param shelf The existing shelf to be updated.
 * @return The updated shelf with the added books.
 */
fun addBooksToShelf(books: List<String>, shelf: MutableList<String>): MutableList<String> {

    // Use the plus assignment operator to add the books to the shelf
    shelf += books
    
    return shelf
}
/**
 * This function takes a list of books and adds them to a shelf.
 * The function uses the plus assignment operator to add the books to the shelf.
 *
 * @param books A list of books to be added to the shelf.
 * @param shelf The existing shelf to be updated.
 * @return The updated shelf with the added books.
 */
fun addBooksToShelf(books: List<String>, shelf: MutableList<String>): MutableList<String> {
/**
 * This function takes a list of books and adds them to a shelf.
 * The function uses the plus assignment operator to add the books to the shelf.
 *
 * @param books A list of books to be added to the shelf.
 * @param shelf The existing shelf to be updated.
 * @return The updated shelf with the added books.
 */
fun addBooksToShelf(books: List<String>, shelf: MutableList<String>): MutableList<String> {

    // Use the plus assignment operator to add the books to the shelf
    shelf += books
    
    return shelf
}