Marc Krasner, "A class of hyperrings and hyperfields", International Journal of Mathematics and Mathematical Sciences, vol. 6, Article ID 240850, 5 pages, 1983. https://doi.org/10.1155/S0161171283000265
A class of hyperrings and hyperfields
Hyperring is a structure generalizing that of a ring, but where the addition is not a composition, but a hypercomposition, i.e., the sum of two elements, , of a hyperring is, in general, not an element but a subset of . When the non-zero elements of a hyperring form a multiplicative group, the hyperring is called a hyperfield, and this structure generalizes that of a field. A certain class of hyperfields (residual hyperfields of valued fields) has been used by the author  as an important technical tool in his theory of approximation of complete valued fields by sequences of such fields. Tne non-commutative theory of hyperrings (particularly Artinian) has been studied in depth by Stratigopoulos .The question arises: How common are hyperrings? We prove in this paper that a conveniently defined quotient of any ring by any normal subgroup of its multiplicative semigroup is always a hyperring which is a hyperfield when is a field. We ask: Are all hyperrings isomorphic to some subhyperring of a hyperring belonging to the class just described?
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