This time we focus on AEB and CED. Viewing AC as a transversal cutting across the parallel line segments AB and DC, we see that 1 2 since they are alternate interior angles to this pair of parallel lines (Figure G.47(a)). Viewing DB as a transversal cutting across the same parallel line segments, we see that 3 4 since they are alternate interior angles to this pair of parallel lines (Figure G.47(b)).