CONTENTS Chapter I. Evaluation in algebraic systems I.1. The concepts of valuation, global validity, and transfer theorem I.2. Heyting algebras and Stone spaces I.3. Definition and examples of valuations I.4. The connection between deducibility and global validity I.5. The connection between validity and global validity I.6. Cancellation of idempotents and transfer theorems in the case of rings. Expressibility of global validity I.7. Universal valuation. The notion of sheaf on a Heyting algebra Chapter II. Localizations and valuations II.1. Local axiomatizability of a class of algebraic systems II.2. Valuation and model completeness. Boolean absoluteness II.3. Macintyre's problem: a model companion of a locally axiomatizable class II.4. A model companion of a class of localizations. The completeness of the theory of a locally axiomatizable class II.5. The transfer of a local theory into a locally axiomatizable class Chapter III. A natural translation of classical into intuitionistic theory for algebras with metric Chapter IV. Heyting completion of locally compact topological spaces Appendix. Evaluation in Boolean algebras References