Taking ABC as the triangle of reference, with the usual notation for its sides and angles, let l = s − a, m = s− b, n = s − c. Let I, I1, I2, I3 be the centres of the inscribed and escribed circles DEF, D1E1F1, D2E2F2, D3E3F3.

Through A, B, C draw parallels to the opposite sides forming the triangle A1B1C1, so that AAl, BB1, CC1 are the medians of the triangle ABC, and there are then ten triangles like ABB1, ACB1, etc., of the same area.