User blog comment:Simply Beautiful Art/Feferman's theta extended to weakly compact cardinals/@comment-35470197-20190825022628/@comment-31663462-20190825120329

It probably makes an ordinal notation. If one were going to try and do such, it would probably rely on deducing the general "nature" of \(\theta_\pi^\alpha(\mu)\) for \(\mu<\alpha\) and then for \(\mu\ge\alpha\).

To the Mahlo OCF, I mentioned that it was a simple fix, since \(\psi\) isn't necessarily to define \(\chi\).