Czapla-Wojtaszek, M., J. Brzostek, and A. Mazur. “Achalasia of the esophageus in a 13-years old girl- a case report”. European Journal of Clinical and Experimental Medicine, vol. 3, no. 3, Sept. 2005, pp. 277–279, https://journals.ur.edu.pl/ejcem/article/view/13457.