User blog comment:PsiCubed2/My attempt for creating an ψ(ψᵢ(0))-level notation for ordinals/@comment-24920136-20170329070238/@comment-30754445-20170406202453

On second thought... one big adventage of using trees is that defining the fundamental sequences is very easy (at least up to ψ(Ωω)). Heck, I can immediately write the fundamental sequence of any Buchholz Hydra even though I have absolutely no idea what tree represents what ordinal.

That's really really cool.