. . . "Finally, a shorter notation equivalent to { n => n + 10 } exists in the form of (_ + 10), which means you do not have to declare the input parameter if it is just implied by the method you???re invoking; in our case n is called an anonymous variable because you can call it anything you like such as x or number, so underscore means a blank you need to fill up with each element of your collect" . .