Let a triangle ABC inscribed in a circle Γ with center O. Let I the incenter of triangle ABC and D,E,F the contact points of the incircle with sides BC,AC,AB of triangle ABC respectively . Let also S the foot of the perpendicular line from D to the line EF.Prove that line SI passes from the antidiametric point N of A in the circle Γ.( AN is a diametre of the circle Γ). geometry unsolvedgeometrycircumcircle