Lines m and n are cut by a transversal, as shown in the figure.

Line l is drawn from the upper left to lower right. Lines m and n are drawn from the upper right to the lower left. Line l intersects line m and lines n. Where line l intersects line m, the angles formed are listed from the top in clockwise order: angle 1, angle 2, angle 3, and angle 4. Where line l intersects line n, the angles formed are listed from the top in clockwise order: angle 5, angle 6, angle 7, and angle 8.

Given line m is not parallel to line n, prove ∠4 is not congruent to ∠6 by contradiction. (2 points for the assumption statement, 4 points for the remainder of the proof)