Question 99
Three equally sized circles $k_{1}$, $k_{2}$, $k_{3}$ intersect non-tangentially at a point $P$. Let $A$ and $B$ be the centers of the circles $k_{1}$ and $k_{2}$. Let $D$ or $C$ be the intersection of $k_{3}$ with $k_{1}$ or $k_{2}$ that is different from $P$. Show that $A B C D$ is a parallelogram.