Array Order Cascading Hyper Notation (AoCHN) is the 12th part of HN.
An expression is of the form H_m<n,A>, where n is the base, m is the secondary base, and A is an array.
As always, the definitions from HCHN apply.
We can define X_n as X<n>, but we define X_A as X<(A)>. And if, in X<A>, A is a limit array, it will be the cascader of X<FS(A,x)>,that means it copies X<FS(A,x)> and not [A]. Else, if A is the sequence array, ignore A except for the first entry and solve like normal.
To compare arrays, use the rules from HCHN and when comparing X<A> and X<B>, compare A and B and that is the result.