User blog comment:Deedlit11/Ordinal Notations V: Up to a weakly Mahlo cardinal/@comment-24509095-20140509071457/@comment-24509095-20140511065540

Also, we can't just say $$\chi(M,1)[n]$$. It must be on a collapsing function: $$\psi_{\chi(M,1)}(0)[n]$$.