Let $A, B, C$ on line $L_1$; $A', B', C'$ on lie $L_2$; $A'', B'', C''$ on line $L_3$. And L1, L2, L3 are concurrent. Such that $AA', BB', CC'$ are concurrent, name the point of concurrence is $M$, and $A'A'', B'B'', C'C''$ are concurrent, name the point of concurrence is $N$
How to prove that $AA'', BB'', CC''$ are concuurent, name the point of concurrence is $P$ and $M, N, P$ are collinear
