Corollary: Parallelogram  Defining Property I
(related to Proposition: 1.34: Opposite Sides and Opposite Angles of Parallelograms)
If both pairs of opposite sides of a 4sided figure are equal in length, it is a parallelogram.
Table of Contents
Proofs: 1
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References
Adapted from CC BYSA 3.0 Sources:
 Callahan, Daniel: "Euclidâ€™s 'Elements' Redux" 2014
Adapted from (Public Domain)
 Casey, John: "The First Six Books of the Elements of Euclid"