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7.26 (1980)

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The ordinal height of a variety of groups is, by definition, the supremum of order types (ordinals) of all well-ordered by inclusion chains of its proper subvarieties. It is clear that its cardinality is either finite or countably infinite, or equal to $\omega_1$. Is every countable ordinal number the ordinal height of some variety?

Contributor: A. V. Kuznetsov

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