Suppose $I,O,H$ are incenter, circumcenter, orthocenter of $\vartriangle ABC$ respectively. Let $D = AI \cap BC$,$E = BI \cap CA$, $F = CI \cap AB$ and $X$ be the orthocenter of $\vartriangle DEF$. Prove that $IX \parallel OH$.
Problem
Source: https://artofproblemsolving.com/community/c6h1740825p11314688
Tags: geometry, incenter, Circumcenter, orthocenter, parallel, Euler Line