Answer
1. By the definition of angle bisector, if CE bisects angle BCD and if BE bisects angle ABC, then angle 1 equals angle two, and angle 3 equals angle 4.
2. Thus, because angle 2 and angle 3 add up to 90 degrees, this means that angle ABC and BCD add up to 180 degrees.
3. If corresponding angles are congruent, it follows that angle BCD is congruent to angle ABC's supplement.
4. Thus, if the corresponding angles are congruent, then ABC and BCD are supplementary.
5. ABC and BCD are supplementary as found in (2), so corresponding angles are congruent.
6. If corresponding angles are congruent, the two lines are parallel.
7. l and n are parallel.
