“…In [1][2][3], we are lucky to obtain complete information about the periodic solutions of (4) when = 1 and = 1, 0, or −1 by breaking the solutions into two sequences, a companion and an error (more specifically, for a solution = { } ∈N of (4) with = 1 and ∈ {−1, 0, 1}, the companion sequence is = { } ∈N which is an even integral sequence so that = 2[(1/2) ], where 2[ /2] is the greatest even integer that is less than or equal to ∈ R, and the error sequence = { } ∈N is defined by = − , ∈ Z).…”