User blog comment:TechKon/Left-right arrow notation/@comment-5150073-20150810092730/@comment-25601061-20150810190353

Define A(a) = a ↑ ↑ ↑... ↑ ↑ ↑a with a arrows

Define AAA...AAA(a) (b A's) = AAA...AA( AAA...AA( AAA...AA(... AAA...AA( AAA...AA( AAA...AA(a) ) ) ) ) ) with a levels and b-1 A's

Define AAA...AAA(a) (b A's) = a ↔b

There.