RIght Lines Parallel to one and the same, are also Parallel the one to the other.
Let the Lines AB, FE, be Parallel to the Line CD; I say they are Paral∣lel the one to the other. Let the Line GK cut all three.
Demonstration. Seeing that the Lines AB, CD, are Parallel; the Alternate Angles AHI, HID, shall be equal (by the 29th:) and because the Lines CD, FE, are also Parallel, the Exteriour Angle HID shall be equal to the In∣teriour ILE (by the same.) Therefore the Alternate Angles AHI, ILE,