User blog comment:O0112111/Uncomputable Number/@comment-35470197-20190927141227

What is A? Any subset of P(N)? Then the notion of a critical point does not make sense because A does not necessarily contain N.

The use of \(\mapsto\) is incorrect. When you describe the domain and the codomain, then you should use \(\to\).

The function itself is ill-defined, because n depends on j, which is unspecified and is not unique.