Abstract. For a semiring S with commutative addition, conditions are considered such that S has nontrivial fc-ideals or maximal fc-ideals, among others, by the help of the congruence class semiring S/A defined by an ideal A of S . Moreover, all maximal A>ideals of the semiring of nonnegative integers are described.
PreliminariesA semiring S is defined as an algebra (S, +, •) such that (S, +) and (S, Finally, an ideal A of S is called trivial, iff A = S holds or A = {0} , the latter clearly if 5 has an absorbing element. To deal with both cases simultaneously, we introduce the notion S' by S' -S\{0} if S has an absorbing element, and S' = S otherwise.•In this paper we only consider semirings S for which (S, +) is commutative. If also (S, •) is commutative, S is called a commutative semiring. Moreover, to avoid trivial exceptions, each semiring S is assumed to have at least two elements.Using only commutativity of addition, the following concepts and statements, essentially due to [1,2,4], are well known. For each ideal A of a semiring S