Cobzaş, Ş. “Non Convex Optimization Problems on Weakly Compact Subsets of Banach Spaces”.
Anal. Numér. Théor. Approx.
, vol. 9, no. 1, Feb. 1980, pp. 19-25,
https://ictp.acad.ro/jnaat/journal/article/view/1980-vol9-no1-art3
.