Straight-lines joining equal and parallel (straight-lines) on the same sides are  themselves also equal and parallel.Let $AB$ and $CD$ be equal and parallel (straight-lines), and let the straight-lines $AC$ and $BD$ join them on the same sides. I say that $AC$ and $BD$ are also equal and parallel. <prf> Thus, straight-lines joining equal and parallel (straight-lines) on the same sides are themselves also equal and parallel.