Published online by Cambridge University Press: 12 March 2014
Among the results of this paper are the following:
1. Every Boolean (ultra)power is the union of an updirected elementary family of direct ultrapowers.
2. Under certain conditions, a finitely iterated Boolean ultrapower is isomorphic to a single Boolean ultrapower.
3. A ω-bounded filtral power is an elementary substructure of a filtral power.
4. Let be an elementary class closed under updirected unions (e.g., if
is an amalgamation class); then
is closed under finite products if and only if
is closed under reduced products if and only if
is a Horn class.