In this paper we analyze Ko's Theorem 3.4 in \cite{Ko87}.
We extend point b) of Ko's Theorem by showing that
\poneh(\upcoup)=\upcoup. As a corollary, we get the equality
\ph(\upcoup) = \poneh(\upcoup), which is, to our knowledge, a
unique result of type \poneh({\cal C})=\ph({\cal C}), for a class C
that would not be equal to \DP.
With regard to point a) of Ko's Theorem, we observe that it also holds for the
classes \upk{k} and for \fewp.
In spite of this, we prove that point b) of Theorem 3.4 fails for such
classes in a relativized world. This is obtained by showing the
relativized separation of \upcoupk{2} from \poneh(\npconp).
Finally, we suggest a natural line of research arising from these facts
