The algebra of many-valued quantities

The general idea of consideringall the limits, and not merely upper and lower limits, seems to have been first utilized by W. H. Young in 1908: “Sulle due funzioni a più valori costituite dai limiti d'una funzione di variabile reale a destra ed a sinistra di ciascun punto”, Rend. Acc. Lincei (5)17, 582–87.Google Scholar