Parts of parallel lines are parallel is a postulate or theorem?

I encountered a proof problem where I was given parallelogram ABCD and that AE is congruent to FC. I had to prove EBFD was a parallelogram. I want to use the theorem that if one pair of sides of a quadrilateral is both congruent and parallel, then it is a parallelogram. In doing so, I would like to say that EB is parallel to FD because parts of parallel lines are parallel. Is that a postulate?http://i900.photobucket.com/albums/a...abcdparall.jpg