1.
Gretskii OS. $ℂ$-differentiability of mappings of Hilbert spaces. Ukr. Mat. Zhurn. [Internet]. 1995 Mar. 25 [cited 2025 Apr. 13];47(3):424–428. Available from:
https://umj.imath.kiev.ua/index.php/umj/article/view/5436