User blog comment:SuperSpruce/The T array function: Part 2: Dimensional Arrays/@comment-38080588-20190222205602/@comment-36984051-20190225162300

You’re missing the point. The subscript is the like the n in f_α(n). Each time you decrement the first number in the brackets, you nest that expression n times, just like how if you decrement the ordinal in the FGH you nest that n times.