We investigate combinations of structures by families of structures relative to families of unary predicates and equivalence relations. Conditions preserving $\omega$-categoricity and Ehrenfeuchtness under these combinations are characterized. The notions of $e$-spectra are introduced and possibilities for $e$-spectra are described.
Closures and generating sets related to combinations of structures
Expansions and restrictions of structures and theories, their hierarchies
Combinations related to classes of finite and countably categorical structures and their theories
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