Densities of ultraproducts of Boolean algebras

by Koppelberg and Shelah. [KpSh:415]
Canadian J Math Journal Canadien de Mathematiques, 1995
We answer three problems by J. D. Monk on cardinal invariants of Boolean algebras. Two of these are whether taking the algebraic density pi (A) resp. the topological density d(A) of a Boolean algebra A commutes with formation of ultraproducts; the third one compares the number of endomorphisms and of ideals of a Boolean algebra.

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