A. 373. P is a point in the interior of the quadrilateral A₁A₂A₃A₄ that does not lie on either diagonal. The points B_i lie in the interior of each line segment A_iP. Let C_ij be the intersection of the lines A_iB_j and A_jB_i (1i<j 4). Prove that the line segments C₁₂C₃₄, C₁₃C₂₄, C₁₄C₂₃ are all concurrent.

(5 points)

Deadline expired.

Statistics on problem A. 373. 4 students sent a solution. 5 points: Pálinkás Csaba, Paulin Roland, Strenner Balázs. 2 points: 1 student.