On the Recursive Enumerability of Fixed-Point Combinators
Mayer Goldberg · BRICS Report Series · 2005
We show that the set of fixed-point combinators forms a recursively-enumerable subset of a larger set of terms we call non-standard fixed-point combinators. These terms are observationally equivalent to fixed-point combinators in any computable context, but the set of on-standard fixed-point combinators is not recursively enumerable.