Let ABC be a triangle and I its incenter. The lines BI and CI intersect the circumcircle of ABC again at M and N, respectively. Let C1 and C2 be the circumferences of diameters NI and MI, respectively. The circle C1 intersects AB at P and Q, and the circle C2 intersects AC at R and S. Show that P, Q, R and S are concyclic. geometryCyclic Quadrilateralstriangle -incentercircumcircle