
doi: 10.1007/bf01191540
handle: 11365/1014122
[Part II is reviewed below.] The authors try to answer the question: How much of the structure involved in congruence modular varieties exists for congruence semimodular (CSM) varieties? They examine locally finite CSM varieties. For any finite algebra \(A\) in a CSM variety, natural congruences \(\underset {T}\sim\) are defined which play a role similar to that played by the commutator for algebras in a congruence modular variety. It is shown that if \(\underset {T} \sim\) is a congruence on the finite algebras of some locally finite CSM variety \(V\), then \(\underset {T} \sim\) induces a congruence \(\underset {T}\simeq\) on the subvariety lattice \(L_ V\) of \(V\). Furthermore, the quotient lattice \(L_ V/\underset {T} \simeq\) is both algebraic and dually algebraic and the natural map of \(L_ V\) onto \(L_ V/\underset {T}\simeq\) is complete (Theorem 4.3). The existence of irredundant subdirect product decomposition in CSM varieties is investigated. Further, it is proved that if \(V\) is a variety with the Congruence Extension Property, then \(V\) is CSM iff the 5-generated free \(V\)-algebra is CSM (Theorem 7.3). Theorem 8.5 states that a locally finite variety \(V\) is geometric iff \(V\) is a varietal product of a strongly Abelian geometric variety and an affine variety whose corresponding ring is finite and semi-simple.
subdirect product decomposition, congruence extension property, Congruence modularity, congruence distributivity, affine variety, semimodular, geometric variety, subvariety lattice, locally finite variety, quotient lattice, congruence semimodular variety
subdirect product decomposition, congruence extension property, Congruence modularity, congruence distributivity, affine variety, semimodular, geometric variety, subvariety lattice, locally finite variety, quotient lattice, congruence semimodular variety
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