User blog comment:Googleaarex/My number is bigger! (Googology Wiki version)/@comment-11227630-20140921010305/@comment-5529393-20140921142748

Let me help Googleaarex out here:

for Arrow(n,m,k), write k in binary, then replace each 1 with an up arrow, and each 0 with a down arrow. That is the expression you put between n and m.