User blog comment:MilkyWay90/I'm ready for the easiest OCF!/@comment-35470197-20180821012104/@comment-30754445-20180821175435

Weak?

For a person who wants to learn the basics of OCFs, even Buchholz's OCF is too strong and too complicated (it also has the disadvantage of being difficult to extend further).

He should start with a single ψ. The OCF mentioned in Fejfo's link is a good start.