Let $ABC$ be an acute, non isosceles triangle with the orthocenter $H$, circumcenter $O$ and $AD$ is the diameter of $(O)$. Suppose that the circle $(AHD)$ meets the lines $AB, AC$ at $F$, respectively. Denote $J, K$ as orthocenter and nine- point center of $AEF$. Prove that $HJ \parallel BC$ and $KO = KH$.