Show that, if the mutual fund separation property holds for \(K=1\), i.e., there exists a portfolio \(w^{*}\) such that \(\mathbb{E}\left[u\left(\tilde{r}_{w^{*}}\right)\right] \geq \mathbb{E}\left[u\left(\tilde{r}_{w}\right)\right]\) for any \(w \in \Delta_{N}\) and for any concave utility function \(u\), then \(w^{*}\) must coincide with the minimum variance portfolio.