Abstract
We introduce four extension properties (CEP, QEP, SCEP and SQEP) for ordered algebras, similar to the congruence extension property (CEP) and the strong congruence extension property of usual (unordered) algebras. All four properties turn out to have a description in terms of commutative squares or pullback diagrams. We then use these categorical descriptions to prove an ordered analogue of the well-known relation TP = AP + CEP, namely that a variety of ordered algebras has the ordered transferability property if and only if it has the ordered amalgamation property and QEP.
Similar content being viewed by others
References
S.L. Bloom, Varieties of ordered algebras. J. Comput. Syst. Sci. 13, 200–212 (1976)
S. Bulman-Fleming, N. Sohail, Examples concerning absolute flatness and amalgamation in pomonoids. Semigroup Forum 80, 272–292 (2010)
G. Czédli, A. Lenkehegyi, On congruence \(n\)-distributivity of ordered algebras, Acta Math. Hung. 41, 17–26 (1983)
G. Czédli, A. Lenkehegyi, On classes of ordered algebras and quasiorder distributivity, Acta Sci. Math. 46, 41–54 (1983)
J.I. Garcia, The congruence extension propery for algebraic semigroups. Semigroup Forum 43, 1–18 (1991)
V. Gould, M. Wild, Every Hamiltonian variety has the congruence extension property—a short proof. Algebra Univers 26, 187–188 (1989)
E.W. Kiss, L. Márki, P. Pröhle, W. Tholen, Categorical algebraic properties. A compendium on amalgamation, congruence extension, epimorphisms, residual smallness, and injectivity. Stud. Sci. Math. Hung. 18, 79–141 (1983)
V. Laan, N. Sohail, On mono- and epimorphisms in varieties of ordered algebras, to appear
Acknowledgments
We are very grateful to Professor George Janelidze for pointing out the idea behind Theorem 4.2. We also wish to thank the referee for useful suggestions. This research was supported by Estonian Institutional Research Project IUT20-57. The second named author is a recepient of the Estonian Science Foundation’s MOBILITAS research grant MJD 198.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Laan, V., Nasir, S. & Tart, L. On congruence extension properties for ordered algebras. Period Math Hung 71, 92–111 (2015). https://doi.org/10.1007/s10998-015-0088-x
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10998-015-0088-x
Keywords
- Ordered algebra
- Order-congruence
- Compatible quasiorder
- Congruence extension property
- Quasiorder extension property
- Amalgamation property
- Transferability property