Start from a triangle t=(ABC) , a point D and a line e. Draw the intersection points A',B',C' on the sides of t of the line (h) through D, parallel to e. Join AA', BB', CC' and build the triangle t'=(A''B''C'') of these lines. Repeat the procedure by replacing t with t'. All these triangles are perspective to t on fixed lines f, g, h, k, which depend only on t, D and e.