Let [math]PQR[/math] be a triangle whose sides [math]QR, RP, PQ[/math] meet the polars [math]p, q, r[/math] of its vertices in points [math]P_1, Q_1, R_1[/math]. The polar of [math]R_1 = PQ\cdot r[/math] is [math]r_1 = (p\cdot q)R[/math]. Define the extra points [math]P' = PQ\cdot q, R' = QR\cdot q[/math], and the polar [math]p'= (p\cdot q)Q[/math] of the former.