Abstract

We consider the theory Thprin of Boolean algebras with a principal ideal, the theory Thmax of Boolean algebras with a maximal ideal, the theory Thac of atomic Boolean algebras with an ideal where the supremum of the ideal exists, and the theory Thsa of atomless Boolean algebras with an ideal where the supremum of the ideal exists. First, we find elementary invariants for Thprin and Thsa. If T is a theory in a first order language and α is a linear order with least element, then we let Sentalg be the Lindenbaum-Tarski algebra with respect to T, and we let intalg be the interval algebra of α. Using rank diagrams, we show that Sentalg ⋍ intalg, Sentalg ⋍ intalg ⋍ Sentalg, and Sentalg ⋍ intalg. For Thmax and Thac we use Ershov's elementary invariants of these theories. We also show that the algebra of formulas of the theory Tx of Boolean algebras with finitely many ideals is atomic