User blog comment:Nedherman1/New Notation Idea/@comment-30754445-20180718024126

f_a is comparable to ω+1 in the FGH.

f_z is comparable to ω+26 in the FGH.

f_z;z is comparable to ω+27 in the FGH. The trick of using "f_z(n)" repetitions instead of n doesn't affect the end result by much.It just means that instead of getting fω+27(n), you get fω+27(fω+26(n)). This is still way smaller than fω+28(n) (which, as you may recall, is fω+27(fω+27(fω+27(...(n)))) with n repetitions).