Question 66
Let $ABCD$ be a convex quadrilateral and let $P$ and $Q$ be points inside the quadrilateral $ABCD$ such that $PQDA$ and $QPBC$ are cyclic quadrilaterals. Suppose that there exists a point $E$ on the segment $PQ$ such that $\angle PAE = \angle QDE$ and $\angle PBE = \angle QCE$. Show that $ABCD$ is a cyclic quadrilateral.