1. Berezansky, L., Braverman, E., Idels, L.: Mackey–Glass model of hematopoiesis with non-monotone feedback: stability, oscillation and control. Appl. Math. Comput. 219, 6268–6283 (2013)
2. Dix, J.G., Padhib, S., Patic, S.: Multiple positive periodic solutions for a nonlinear first order functional difference equation. J. Differ. Equ. Appl. 16, 1037–1046 (2010)
3. Jiang, D., O’Regan, D., Agarwal, R.P.: Optimal existence theory for single and multiple positive periodic solutions to functional difference equations. Appl. Math. Comput. 161, 441–462 (2005)
4. Li, Z.-X., Wang, X.: Existence of positive periodic solutions for neutral functional differential equations. Electron. J. Differ. Equ. 2006, No. 34 (2006)
5. Mackey, M.C., Glass, L.: Oscillation and chaos in physiological control system. Science (New Series) 197, 287–289 (1977)