Theorems 3-1 Through 3-10

theorem 3-1 : if two parallel planes are cut by a third plane, then the lines of intersection are parallel.

postulate 10 : if two parallel lines are cut by a transversal, then correspondong angles are congruent.

theorem 3-5 : if two lines are cut by a transversal and alternate interior angles are congruent, then the lines are parallel.

theorem 3-6 : if two lines, are cut by a transversal and same-side interior angles are supplementary, then the limes are parallel.