Question 151
Let $ABC$ be a non-isosceles triangle with altitudes $AD$, $BE$, $CF$ concurrent at $H$. Denote $K$, $M$ as the midpoints of $AH$, $BC$ and $BK$ meets $AM$ at $L$. On $AC$, take $I$ such that $OI \parallel BC$ and $DE$ meets $IK$ at $S$. Prove that $L$, $K$, $S$, $E$ are concyclic.