H_(i, j) = H_(i - 1, j + 1)

rank | Hankel matrix 1 | (a) 2 | (a | b b | c) 3 | (a | b | c b | c | d c | d | e) 4 | (a | b | c | d b | c | d | e c | d | e | f d | e | f | g)

symmetric