Give the definition of what it means for a sequence \((x_{n})\) in a Banach space \(X\) to
converge weakly to \(x \in X\).
Let \(X = [0, 1]\) equipped with the Lebesgue measure. For \(n =\) 1, 2, …, let \(f_{n} = n \cdot \chi _{[0,1/n]}\), where \(\chi _{A}\) denotes
the indicator function for the set \(A\). Prove that the sequence \(f_{n}\) does not
converge weakly to 0 in \(L^{1}([0, 1])\).