User blog comment:Alejandro Magno/Extended Arrow Notation/@comment-10429372-20140919073818/@comment-190.96.244.52-20140919175832

Actually, that is not possible.

There are not 4-entry arrows.

a^(^(m)^(n)^(m)^)^b is a shorcut for a^(^^^...^^^(n)^^^...^^^)^b, where there are m arrows before (n).