User blog comment:Wythagoras/All my stuff/@comment-5029411-20130709033507

4 Rule FGH:

f0(a) = a+1

f@+1(a) = f@^a(a)

f@w^(@+1)*b+1(a) = f@w^(@+1)*b+w^@(a)

f@phi(@+1,b+1)(a) = f@phi(@,phi...(@,phi(@+1,b)+1)...)(a) (a+1 phi's)

Y(4) = fgamma(0)(4)