Reason 4 = SAS congruence property
This is because we have two pairs of congruent sides (AB = CD and AC = CA) with a pair of congruent angles between them. Those angles are the alternate interior angles BAC and DCA
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Reason 6 = Alternate interior angles theorem converse
Similar to reason 2, but the converse means we go in reverse more or less. The original theorem states that if we have parallel lines, then the alternate interior angles are congruent. This time we know the alternate interior angles are congruent, so we conclude the lines are parallel.