DenysenkoO. M., and ParasyukI. O. “Construction of Floquet–Bloch Solutions and Estimation of Lengths of Resonance Zones of One-Dimensional Schrödinger Equation With Smooth Potential”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, no. 1, Jan. 2004, pp. 3-18, https://umj.imath.kiev.ua/index.php/umj/article/view/3724.