[quote name='sooner123' timestamp='1311953556' post='4842187']
Then one kid (who wants to be a mathematician) gave (as by far the winning answer):
[font="Georgia"]f[sub]?_G[/sub](G)[/font]
He even defined the wainer and veblen hierarchies, and graham's number (and the definition for knuth's up-arrows)
Needless to say I was very impressed. Especially seeing how I had to do some pretty hefty research only to figure out what the feferman-schutte ordinal was and if it could actually be used in the diagonalization function.
Pretty good answers, this is high school?
I'll admit I have absolutely no idea what the above function means. Anyone care to elaborate on it?
[/quote]
Happy to.
f[sub]0[/sub](n) = n + 1
f[sub]a+1[/sub](n) = f[sub]a[/sub][sup]n[/sup](n)
f[sub]a[/sub](n) = f[sub]a[n][/sub](n), if a is a limit ordinal
limit ordinals are ordinals that are basically supremums. example: omega (the smallest countable infinity) = supremum (1, 2, 3, 4, ... ad infinitum)
so for example
f[sub]1[/sub](n) = 2n
f[sub]2[/sub](n) = n*2[sup]n[/sup]
and so on
for f[font=sans-serif][size=2][/font][font=sans-serif][size=2]? is. [/font][font=sans-serif][size=2]? = {1 ,2, 3, ...}. so the nth element is n[/font]
[font=sans-serif][size=2]so f[/font][font=sans-serif][size=2]?(n) = f[sub]n[/sub](n)[/font]
[font="sans-serif"]at this level, we're dealing with a function that is on the order of iterated
knuth's arrows[/font]
[font="sans-serif"]f[/font][font=sans-serif][size=2]?[sup]2[/sup](n) is on the order of iterated
conway's chained arrows[/font]
epsilon nought is the supremum of the tetrations of omega: {[font=sans-serif][size=2]?, [/font][font=sans-serif][size=2]?^[/font][font=sans-serif][size=2]?, [/font][font=sans-serif][size=2]?^[/font][font=sans-serif][size=2]?^[/font][font=sans-serif][size=2]?, ...}[/font]
[font="sans-serif"]epsilon_1 is the supremum of the tetrations of epsilon_nought[/font]
[font="sans-serif"]epsilon_(a+1) is the supremum of the tetrations of epsilon_a[/font]
[font="sans-serif"]zeta nought is the supremum of the nested subscripting of episilon nought: supremum {epsilon_nought, epsilon_(epsilon_nought), epsilon_(epsilon_(epsilon_nought)), ...}[/font]
[font="sans-serif"]generalizing this progression from omega to epsilon to zeta, we get the bivariate phi function. taking the supremum of phi's fixed points we get the trivariate, the first fixed point of which is [/font][font=Georgia][size=2]?_0 [/font][font="sans-serif"]which is known as the ferman-schutte ordinal which (i think) is the largest named countably infinite ordinal. it's used as the proof theoretic strength of a bunch of techniques and mathematical frameworks like transfinite recursion.[/font]
[font="sans-serif"]
[/font]
[font="sans-serif"]anyways, evaluating the fundamental sequence for the ordinal this kid gave is perfectly finite, but pretty much unimaginable. it makes graham's number look like planck's constant.. to some unimaginable power.[/font]