Let $ABCD$ be a rectangle with center $O$ such that $\angle DAC = 60^o$. Bisector of $\angle DAC$ cuts a $DC$ at $S$, $OS$ and $AD$ intersect at $L$, $BL$ and $AC$ intersect at $M$. Prove that $SM \parallel CL$.
Problem
Source: OLCOMA Costa Rica National Olympiad, Final Round, 2013 Shortlist G3 day1
Tags: geometry, rectangle