User blog comment:Syst3ms/Breadth-Recursive Array Notation (BRAN)/@comment-25601061-20180424215049/@comment-35392788-20180426180816

We expand it the same way as any other array.

$$A_n(a,b,c,\ldots,z) = A_n(A_n(a,b-1,c,\ldots,z),A_n(a,b,c-1,\ldots,z),\ldots,A_n(a,b,c,\ldots,z-1))$$