[1] E. ASPLUND R. T. ROCKAFELLAR: 
Gradients of convex functions. Trans. Amer. Math. Soc. 139 (1969), 443-467. 
MR 0240621[2] D. F. CUDIA: 
The geometry of Banach spaces. Smoothness. Trans. Amer.  Math. Soc. 110 (1964), 284-314. 
MR 0163143 | 
Zbl 0123.30701[3] A. BRØNDSTED: 
Conjugate convex functions in topological vector spaces. Mat.-Fys. Medd. Danske. Vid. Selsk. 34 (1964), 1-26. 
MR 0166580[4] M. M. VAJNBERG: Variacionnyj metod i meted monotonnych operatorov. Moskva 1972.
[5] W. V. PETRYSHYN: 
A characterization of strict convexity of Banach spaces and other uses of duality mappings. Journ. of Funct. Analysis 6 (1970), 282-291. 
MR 0287289 | 
Zbl 0199.44004[7] V. L. ŠMULIAN: 
Sur la dérivabilité de la norme dans l'espace de Banach. Dokl. Akad. Nauk SSSR 27 (1940), 643-648. 
MR 0002704 | 
Zbl 0023.32604[8] J. J. MOREAU: 
Sur la fonction polaire d'une fonction semi-continue supérieurement. C.R. Acad. Sci. Paris 258 (1964), 1128-1130. 
MR 0160093[9] E. MICHAEL: 
Continuous selection. I. Annals of Math. 63 (1956), 361-382. 
MR 0077107