Through any point in space, there is exactly one straight line Parallel to a given straight line. This Axiom is equivalent to the Parallel Axiom.
See also Parallel Axiom
Dunham, W. ``Hippocrates' Quadrature of the Lune.'' Ch. 1 in
Journey Through Genius: The Great Theorems of Mathematics. New York: Wiley, p. 54, 1990.