Question

Let be a nonempty conver set in a vector space X, and let ro € 22. Assume furthermore that core(12) # 0. Then 2 and {xo} can be separated if and only if they can be properly separated. Proof. It suffices to prove that if N and {30} can be separated, then they can be properly separated. Choose a nonzero linear function f: X → R such that f(x) < f(xo) for all re. = Let us show that there exists w El such that f(w) < f(20). Suppose on the contrary that this is not the case. Then f(x) = f(xo) for all x E 12. Since core(52) = 0, by Lemma 2.47, the function f is the zero function. This contradiction completes the proof of the proposition.

Answer 1

Answer: This passage appears to be a proof of a proposition in functional analysis. The proposition states that if a nonempty convex set N and a singleton set {x0​} in a vector space X can be separated, then they can be properly separated, provided that the core of N is nonempty. The proof proceeds by assuming that N and {x0​} can be separated by a nonzero linear function f, and then showing that there must exist an element w∈N such that f(w)<f(x0​). This is done by assuming the contrary and deriving a contradiction using Lemma 2.47, which states that if the core of a convex set is nonempty, then any linear function that is constant on the set must be the zero function. The contradiction shows that the assumption is false, and therefore there must exist an element w∈N such that f(w)<f(x0​), which means that N and {x0​} can be properly separated.

Explanation: