We defined the operation of concatenation for sets of strings on page 10 in the textbook as: ab = {xy | x element a and y element b} are the regular sets closed under concatenation? in other words, if a and b are regular sets, is ab guaranteed to be a regular set? prove or show a counterexample.

well cos like a ds it doesn't really die out, unlike for example, fifa, they always come out with a new version, so lets say your fifa 18 is charging you to update the teams and stuff, so, if messi were to go to real madrid (never gonna happen) it would switch messi to the other team, until the owners of fifa come out with fifa 19, then the game would eventually stop updating, and back to the ds, it doesn't really stop working after sometime because there's lots of things that it could be used for, and idk if u know what i'm saying, but long story short, samsung, represents the ds, if they still work, and people love them but not the new version, the old version still works, so they don't really force people to buy new phones, get me?