In this exercise, you are determing whether or not a given string is "bookended" by a substring. A string is bookended if the beginning characters of the string are the same as the ending characters. Your function should return the largest bookend from any given string. We'll call this function bookends$().$ For example:

bookends$("")$ should return $""$

bookends$("$qq$")$ should return $"$q$"$

bookends$("$abcqwertyabc$")$ should return "abc"

Starter code and tests have been provided for you.