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Atom-canonicity in varieties of cylindric algebras with applications to omitting types in multi-modal logic
Published in Journal of Applied Non-Classical Logics, 2020
Tarek Sayed Ahmed
The last result generalises to infinite dimensions replacing finite axiomatisation by axiomatised by a finite schema (Henkin et al., 1985; Hirsch & Sayed Ahmed, 2014). We consider relation algebras as algebras of the form , where is a Boolean algebra , ⌣ is a unary operation and; is a binary operation. A relation algebra is representable⇔ it is isomorphic to a subalgebra of the form , where X is an equivalence relation, is interpreted as the identity relation, ⌣ is the operation of forming converses, and; is interpreted as composition of relations. Following standard notation, denotes the class of (representable) relation algebras. The class is a discriminator variety that is finitely axiomatisable, cf. Hirsch and Hodkinson (2002, Definition 3.8, Theorems 3.19). All of the above classes of algebras are instances of s. The action of the non-Boolean operators in a completely additive (where operators distribute over arbitrary joins component-wise) atomic , is determined by their behaviour over the atoms, and this in turn is encoded by the atom structure of the algebra.