User blog comment:MachineGunSuper/Updated Exploding Fast Growing-Hierarchy/@comment-34812936-20180228070920/@comment-30754445-20180228111109

It's not a seperate rule. It's the same rule, just explicitly stated for a=1:

" ₰1(n) = ₰0(n) is iterated n+1 times "

and

" ₰1(n) = ₰0(₰0(₰0(...(n)...)) with ₰0 (n) iterations "

Is exactly the same thing, because ₰0(n) = n+1.