Karataeva, T. V. “On the Existence of a Mixed Sum of Additive Systems”.
Ukrains’kyi Matematychnyi Zhurnal
46, no. 6 (June 25, 1994): 699–707. Accessed April 11, 2025.
https://umj.imath.kiev.ua/index.php/umj/article/view/5697
.