An Omitting Types Theorem for first order logic with infinitary relation symbols

In this paper, an extension of first order logic is introduced. In such logics atomic formulas may have infinite lengths. An Omitting Types Theorem is proved. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A simple construction of representable relation algebras with non‐representable completions

We give a simple new construction of representable relation algebras with non‐representable completions. Using variations on our construction, we show that the elementary closure of the class of completely representable relation algebras is not finitely axiomatizable (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)