Higher Order Cascading Hyper Notation (HCHN) is the 11th 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 NCHN apply.
X_1 = X.
Define [A] is first order block, and X is cascader for first order block.
Define H_X<X,A> is second order block, and X_2 is cascader for second order block. That means X_2 copies H_X<X,A> and not [A].
Define H_X_(B-1)<X_(B-1),A> (where B is sequence array) is (B-1)th order block, and X_B is cascader for (B-1)th order block. That means X_B copies H_X_(B-1)<X_(B-1),A> and not [A] or H_X_C<X_C,A> (where C can be any array that smaller than B)
Finally, the nth member of X_A's FS (where A is limit array) is X_FS(A,n).
To compare arrays, use NCHN rules, and if you need to compare X_A and X_B, compare A and B, and that is the result.