Bell inequalities are an important tool in device-independent quantum information processing because their violation can serve as a certificate of relevant quantum properties. Probably the best known example of a Bell inequality is due to Clauser. Horne. Shimony and Holt (CHSH). https://www.spidertattooz.com/The-GelBottle-Inc-BIAB-Gel-Polish-Spirited-67oz-p17706/