User blog comment:MilkyWay90/I'm ready for the easiest OCF!/@comment-35470197-20180821012104/@comment-35470197-20180824234851

@Chronolegends

Although it is much simpler than theta functions, it might be a little more complicated than other non-indexed psi functions for beginners who are not familiar with usual mathematics, because they need to consider simultaneously infinitely many new functions.

On the other hand, Buchholz' psi tells us how cardinals separate ordinals into distinct stages, thanks to the index. So there are both merits and demerits.