User blog comment:Deedlit11/Is BEAF well-defined?/@comment-25418284-20121121205547/@comment-5150073-20121122084848

Chris Bird proposed symbols [1 \ 2], [1 \ 1 \ 2], [1 \ 1 \ 1 \ 2], and used them as an approximation for tetrational, pentational and hexational arrays respectively. Moreover, he compares his symbols to fast-growing hierarchy.

As I undestand, tetrational arrays has level Epsilon 0, pentational = Zeta 0, hexational = Eta 0, and {a,b,c} ranges has level phi(w,0) (w is omega there).