文摘
We provide a short proof of the following fact: If X is a Banach space, A and B are bounded, closed and convex sets with dist(A,B)>0dist(A,B)>0 and every x⁎∈X⁎x⁎∈X⁎ with the property that sup(x⁎,B)<inf(x⁎,A)sup(x⁎,B)<inf(x⁎,A) attains its infimum on A and its supremum on B, then both A and B are weakly compact.