If two straight lines joined to one another are parallel (respectively) to two straight lines joined to one another, which are not in the same plane, then the planes through them are parallel (to one another). * For let the two straight lines joined to one another, $AB$ and $BC$, be parallel to the two straight lines joined to one another, $DE$ and $EF$ (respectively), not being in the same plane. * I say that the planes through $AB$, $BC$ and $DE$, $EF$ will not meet one another (when) produced.
(not yet contributed)
Proofs: 1