“…But the other limit k → 0 may be considered as it allows the shrinking of the region (−x 0 , x 0 ) up to a finite interval (−1, 1). The general solutions of equation (2.21) for arbitrary energy E, which we need, was obtained only recently in Ref [57,58]. Here we will not describe the method of obtaining these solutions, but for readers' convenience, we have included a self-contained brief introduction about elliptic functions in Appendix A.…”