Gretskii, O.S. (1994) “On the ?-differentiability of mappings of Banach spaces”,
Ukrains’kyi Matematychnyi Zhurnal
, 46(10), pp. 1336–1342. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/5612
(Accessed: 10 April 2025).