2. The property
Lemma 1. Let ABC be an isosceles triangle with AB = BC. Let D be a point on the ray BC and let h be the ray obtained by reflecting the ray AD in the line AC. Then the ray h cuts the ray BC in a point E which lies outside the segment BC if the point D lies inside this segment (see Figure 1) and inside the segment BC if the point D lies outside (see Figure 2).