## Solomon Feferman

Department of Mathematics

Stanford University

Stanford

CA 94305-2125 USA

sf@csli.stanford.edu

http://math.Stanford.EDU/~feferman/

### Abstract

A theorem obtained by van Benthem for preservation of formulas under Chu transforms between Chu spaces is strengthened and derived from a general many-sorted interpolation theorem. The latter has been established both by proof-theoretic and model-theoretic methods; there is some discussion as to how these methods compare and what languages they apply to. In the conclusion, several further questions are raised.

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