 This is always (at every iterations) true only for left and right sites.The ingredients are the four block operators and the four universe-block operators, which at the first iteration are formula_38 matrices, the three left-site spin operators and the three right-site spin operators, which are always formula_38 matrices.The Hamiltonian matrix of the "superblock" (the chain), which at the first iteration has only four sites, is formed by these operators.