Suppose that I is incenter of triangle ABC and l′ is a line tangent to the incircle. Let l be another line such that intersects AB,AC,BC respectively at C′,B′,A′. We draw a tangent from A′ to the incircle other than BC, and this line intersects with l′ at A1. B1,C1 are similarly defined. Prove that AA1,BB1,CC1 are concurrent. geometryincenterprojective geometrygeometry proposed