User blog comment:TechKon/Left-right arrow notation/@comment-5150073-20150810092730/@comment-25601061-20150813210340

↔ ↑

Define a ↔1 = a ↑ ↑ ↑... ↑ ↑ ↑a with a arrows

Define 1,a ↔b =  a ↔1

Define c,a ↔b = (c-1,a ↔b),a ↔b-1

Define a ↔b = a,a ↔b.