<P> Note: This follows directly from Euclid's parallel postulate . Further, if the angles of one pair are congruent, then the angles of each of the other pairs are also congruent . In our images with parallel lines, corresponding angle pairs are: α = α1, β = β1, γ = γ1 and δ = δ1 . </P> <P> Alternate angles are the four pairs of angles that: </P> <Ul> <Li> have distinct vertex points, </Li> <Li> lie on opposite sides of the transversal and </Li> <Li> both angles are interior or both angles are exterior . </Li> </Ul> <Li> have distinct vertex points, </Li>

Interior angles that lie on opposite sides of the transversal
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