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Finite Covers, Cohomology and Homogeneous Structures
Author(s) -
Ivanov A. A.
Publication year - 1999
Publication title -
proceedings of the london mathematical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.899
H-Index - 65
eISSN - 1460-244X
pISSN - 0024-6115
DOI - 10.1112/s002461159900163x
Subject(s) - mathematics , homogeneous , cohomology , pure mathematics , combinatorics
In the paper we study finite covers of countable ω‐categorical structures by means of ω‐categorical expansions of bases. It is shown that the cohomology approach of P. Cameron to two‐graphs can be applied to covers of some wide class of structures. For example, it works for some reducts of orderings and hypergraphs. The finite covers of the countable highly homogeneous structures and the reducts of the countable random graph are classified. 1991 Mathematics Subject Classification : 03C45, 05C80.