On a general saddle-point condition in normed spaces

citation_title=Convex analysis; citation_publication_date=1970; citation_id=CR1; citation_author=R.T. Rockafellar; citation_publisher=Princeton University Press citation_title=Optimization by vector space methods; citation_publication_date=1969; citation_id=CR2; citation_author=David G. Luenberger; citation_publisher=Wiley citation_title= , part I; citation_publication_date=1957; citation_id=CR3; citation_author=N. Dunford; citation_author=J.T. Schwartz; citation_publisher=Interscience