“…We remark that p(l, m), q(l, m), r(l, m), s(l, m) in Ξ(l, m) correspond to the types of paths described above in terms of P and Q, respectively. A similar argument can be seen in the proof of Theorem 2.1 of Böhm [7]. On the other hand, for the quantum walk case, this proof appears in Konno [15].…”