Algebra universalis

, Volume 65, Issue 3, pp 285–298 | Cite as

Algebraic lattices and locally finitely presentable categories

  • Hans-E. Porst


We show that subobjects and quotients respectively of any object K in a locally finitely presentable category form an algebraic lattice. The same holds for the internal equivalence relations on K. In fact, these results turn out to be—at least in the case of subobjects—nothing but simple consequences of well known closure properties of the classes of locally finitely presentable categories and accessible categories, respectively. We thus get a completely categorical explanation of the well known fact that the subobject- and congruence lattices of algebras in finitary varieties are algebraic. Moreover we also obtain new natural examples: in particular, for any (not necessarily finitary) polynomial set-functor F, the subcoalgebras of an F-coalgebra form an algebraic lattice; the same holds for the lattices of regular congruences and quotients of these F-coalgebras.

2010 Mathematics Subject Classification

Primary: 08A30 Secondary: 18C35 18B35 

Key words and phrases

algebraic lattice locally finitely presentable category subobject quotient internal equivalence relation congruence 


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Copyright information

© Springer Basel AG 2011

Authors and Affiliations

  1. 1.Department of Mathematics and Computer ScienceUniversity of BremenBremenGermany
  2. 2.Department of Mathematics and StatisticsTshwane University of TechnologyPretoriaSouth Africa

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