algebra universalis

, Volume 55, Issue 2–3, pp 213–226 | Cite as

The Mysterious 2-Crown

  • Richard N. Ball
  • Aleš Pultr
  • Jiří Sichler


We show that the 2-crown is not coproductive, which is to say that the class of those bounded distributive lattices whose Priestley spaces lack any copy of the 2-crown is not productive. We do this by first exhibiting a general construction to handle questions of this sort. We then use a particular instance of this constrution, along with some of the combinatorial features of projective planes, to show that the 2-crown is not coproductive.

2000 Mathematics Subject Classification.

Primary 06D55, 06A11, 54F05 Secondary 06D20, 03C05 

Key words and phrases.

distributive lattice Priestley duality poset first-order definable 


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Copyright information

© Birkhäuser Verlag, Basel 2007

Authors and Affiliations

  1. 1.Department of MathematicsUniversity of DenverDenverUSA
  2. 2.Department of Applied Mathematics and ITI, MFFCharles UniversityPraha 1Czech Republic
  3. 3.Department of MathematicsUniversity of ManitobaWinnipegCanada

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