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The paper extends equirecursion up to FOmega, based on TAPL’s framework, but decidability is restricted to a fragment. A reviewer suggested us this language would be best used as a target language for elaboration, but the source language would be still an open question...
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Yeah, anything that I use will have to extend up to CoC (with or without totality checking). I'm guessing equirecursive types at that level would still be beyond our reach?
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Yes, also because inductive types and recursive types aren't quite the same thing (though it's only obvious in PFPL's presentation). I confess the soundness proofs were Cai's work, and I don't understand them well enough to speculate on extensions.
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