Problem

Source: Brazil EGMO TST2 2023 #3

Tags: geometry, circumcircle, Circumcenter, incenter, incircle, concurrency



Let ΔABC be a triangle and L be the foot of the bisector of A. Let O1 and O2 be the circumcenters of ABL and ACL respectively and let B1 and C1 be the projections of C and B through the bisectors of the angles B and C respectively. The incircle of ΔABC touches AC and AB at points B0 and C0 respectively and the bisectors of angles B and C meet the perpendicular bisector of AL at points Q and P respectively. Prove that the five lines PC0,QB0,O1C1,O2B1 and BC are all concurrent.