Question 92
Let $\mathcal C,\mathcal C'$ be two circles exterior to each other, with centers $O,O'$. Draw parallel radii $OM,O'M'$ with the same direction, and another pair $OP,O'P'$ likewise. Line $MM'$ meets $\mathcal C'$ again at $N$, and line $PP'$ meets it again at $Q$. Prove that $M,N,P,Q$ are concyclic.