I have a question on the arithmetic hierarchy. Suppose I have a relation $R\in\Delta_{m}$, is it true that the set $$ x\in A\iff\exists y R(x,y) $$ lies in $\Sigma_m$?
2026-03-24 23:55:12.1774396512
Characterisation of $\Sigma_m$ in the Arithmetic hierarchy.
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