Question 11
Given a convex $n$-gon ($n \ge 5$) $\Omega: P_1P_2...P_n$, of which no three diagonals are concurrent inside $\Omega$. Prove that one can choose a point inside every quadrilateral $P_iP_jP_kP_l$ ($1 \le i \lt j \lt k \lt l \le n$) and not on any diagonal of $\Omega$, such that the $C_n^4$ points obtained are distinct and the segment connecting any two of them intersects with at least one diagonal of $\Omega$.
(Contributed by Leng Fusheng)
(Contributed by Leng Fusheng)