Article:
Samuel R. Buss.
"A Conservation Result Concerning Bounded Theories and the
Collection Axiom.
Proceedings of the American Mathematic Society
100 (1987) 709-716.
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Abstract We present two proofs, one proof-theoretic and one model-theoretic, showing that adding the BΣ10-collection axioms to any bounded first-order theory R of arithmetic yields an extension which is ∀Σ10-conservative over R.