User blog comment:XXxKennyDashxXx/Basic Separator Matrix Notation/@comment-24920136-20161023211112/@comment-25291678-20161112031823

Actually, a(0)(a(0)a)a = f_4(f_4(a)).

a(0)a(0)a = a(0)(a(0(a(0(a....(0)a)))...))a.