Search for: [Abstract = "In this paper, by defining a pair of classical sets as a relative set, an extension of the classical set algebra which is a counterpart of Belnap's four\-valued logic is achieved. Every relative set partitions all objects into four distinct regions corresponding to four truth\-values of Belnap's logic. Like truth\-values of Belnap's logic, relative sets have two orderings\; one is an order of inclusion and the other is an order of knowledge or information."]

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