I wish to call attention to the value, for some purposes, ot the notation for the ratio ; and for the cross-ratio .

For instance: in Menelaus’ theorem for the property of a transversal meeting the sides of a triangle ABC in the points P, Q, R, the first mentioned notation makes the property shine out very clearly The equation in the form is

,

which conspicuously separates the points on the transversal from the angular points of the triangle.