Abstract
A sentence is -conservative over if <!-- MATH $T + \varphi \vdash \psi$ --> implies <!-- MATH $T \vdash \psi$ --> for every <!-- MATH $\psi \in \Gamma$ --> . In §1 this concept for <!-- MATH $\Gamma = \sum _{n + 1}^0$ --> and <!-- MATH $\prod _{n + 1}^0$ --> is investigated. In §2 results from §1 are applied to interpretability in theories containing arithmetic.

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