Online research in philosophy

We show that a formula φ(x, y) is stable if and only if φ is the pairing map on the unit ball of E x E * , where E is a reflexive Banach space. The result remains true if the formula φ is replaced by a set of formulas $p(\bar{x},\bar{y})$.

The role played by real-valued functions in functional analysis is fundamental. One often considers metrics, or seminorms, or linear functionals, to mention some important examples. We introduce the notion of definable real-valued function in functional analysis: a real-valued function f defined on a structure of functional analysis is definable if it can be "approximated" by formulas which do not involve f. We characterize definability of real-valued functions in terms of a purely topological condition which does not involve logic.

We introduce the concepts of Morley rank and Morley degree for structures based on Banach spaces. We characterize ω-stability in terms of Morley rank, and prove the existence of prime models for ω-stable theories.