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5. Isomorphism problems in a variety


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      Problem 5.1.

      Is every $\Sigma^0_2$ equivalence relation on $\omega$ which is a quotient of $=^{ce}$ actually $\Delta^0_2$?

      Fix a variety. Consider the equivalence on the c.e. sets by isomorphisms of the correspondingly recursively presented object in the variety. What is the complexity of this equivalence relation as a function of the variety?

          Cite this as: AimPL: Invariant descriptive computability theory, available at http://aimpl.org/invdesccomp.