Page:First six books of the elements of Euclid 1847 Byrne.djvu/65

TRAIGHT lines () which are parallel to the same straight line (), are parallel to one another.

Let intersect $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$;

Then, = = (pr. 29.),

∴ =

∴ || (pr. 27.)

Q. E. D.