User blog comment:Kyodaisuu/English description of Fish numbers/@comment-25418284-20131102173245/@comment-24061664-20131103144932

let i=10^90 and j=10^100. What I prooved is that you can't write Rayo(Rayo(10^90)) in 10^100 characters FOST. Do you agree? Even if you can write Rayo function in FOST, you  expression which produce Rayo(Rayo(10^90)) in 10^100 is excluded. Therefore, FOST can't effectively write Rayo^2 function.