| Abstract: | We deal with problems associated with Scott ranks of Boolean algebras. The Scott rank can be treated as some measure of complexity
of an algebraic system. Our aim is to propound and justify the procedure which, given any countable Boolean algebra, will
allow us to construct a Boolean algebra of a small Scott rank that has the same natural algebraic complexity as has the initial
algebra. In particular, we show that the Scott rank does not always serve as a good measure of complexity for the class of
Boolean algebras. We also study into the question as to whether or not a Boolean algebra of a big Scott rank can be decomposed
into direct summands with intermediate ranks. Examples are furnished in which Boolean algebras have an arbitrarily big Scott
rank such that direct summands in them either have a same rank or a fixed small one, and summands of intermediate ranks are
altogether missing. This series of examples indicates, in particular, that there may be no nontrivial mutual evaluations for
the Scott and Frechet ranks on a class of countable Boolean algebras.
Supported by RFFR grant No. 99-01-00485, by a grant for Young Scientists from SO RAN, 1997, and by the Federal Research Program
(FRP) “Integration”.
Translated fromAlgebra i Logika, Vol. 38, No. 6, pp. 643–666, November–December, 1999. |
