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Some Obstacles to Duality in Topological Algebra
Published online by Cambridge University Press: 20 November 2018
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0. Introduction. Functors form an equivalence of categories (see [8,]) if Γ(Φ(A)) ≅ A and Φ (Γ(B)) ≅ B naturally for all objects A from
and B from
. Letting
denote the opposite of
we say that
and
are dual if there is an equivalence between
and
.
Let τ be a similarity type of finitary operation symbols. We let Lτ denote the first order language (with equality) using nonlogical symbols from τ, and consider the class of all algebras of type τ as a category by declaring the morphisms to be all homomorphisms in the usual sense (i.e., those functions preserving the atomic sentences of Lτ). If
is a class in
(i.e.,
and
is closed under isomorphism), we view
as a full subcategory of
, and we define the order of
to be the number of symbols occurring in τ.
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- Copyright © Canadian Mathematical Society 1982