If l1 and l2 are lines are lines on the plane such that they are parallel transports along a transversal l, then they are parallel transports along any transversal.
Use the above theorem to prove that the interior angle sum of a triangle is 180.
If l1 and l2 are lines are lines on the plane such that they are parallel transports along a transversal l, then they are parallel transports along any transversal.
Use the above theorem to prove that the interior angle sum of a triangle is 180.