Omitting Types for Infinitary Real-Valued Logic: A Topological Perspective

Abstract

For countable vocabularies, we extend the omitting types theorem for countable fragments of infinitary logic to Keisler's general real-valued structures by proving that the space of Henkin types of each such fragment is Čech-complete. The structures interpret function symbols arbitrarily and predicate symbols by bounded real-valued functions, while each formula carries a bound of its own. This extends the setting of Eagle's theorem from metric structures with a prescribed master metric to general structures whose vocabulary prescribes the sorts and bounds of the symbols. Following Keisler and Miller's treatment of logic without equality, we build models from closed terms. Morley's Baire category method then gives every satisfiable theory on a countable fragment a model with countable sorts omitting any countable family of types whose closed-term instances have empty interior in the space of Henkin types satisfying the theory.