User blog comment:Scorcher007/Analysis DAN up to Z2/@comment-11227630-20180919121102/@comment-31580368-20180919125621

Yes, but do not forget that in a possible collapsing function, it will only act as a diagonalizer for something like sup{S[a+1]), S[(OCFa(S[b+1])])], S[(OCFa(S[(OCFb(S[c+1])])])])], ...} - it's not that big.