In computability theory two sets ${\displaystyle A;B\subseteq \mathbb {N} }$ of natural numbers are computably isomorphic or recursively isomorphic if there exists a total bijective computable function ${\displaystyle f\colon \mathbb {N} \to \mathbb {N} }$ with ${\displaystyle f(A)=B}$. By the Myhill isomorphism theorem, the relation of computable isomorphism coincides with the relation of mutual one-one reducibility.

Two numberings ${\displaystyle \nu }$ and ${\displaystyle \mu }$ are called computably isomorphic if there exists a computable bijection ${\displaystyle f}$ so that ${\displaystyle \nu =\mu \circ f}$

Computably isomorphic numberings induce the same notion of computability on a set.