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Definition 23

Parallel straight lines are straight lines which, being in the same plane and being produced indefinitely in both directions, do not meet one another in either direction.

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| This definition only defines what it means for straight lines to be parallel; it does not say that there are any parallel lines. Proposition I.31 gives a construction for a line parallel to a given line through a given point.

Book I Introduction - Definitions 22 - Postulate 1.

© 1996
D.E.Joyce
Clark University