H
E
E
L
E
M
E
N
T
S
through E
let EH be drawn parallel to either AB of CD,
and through F
let FK be drawn parallel to either AD or BC; [I.31]
therefore
each of the figures AK, KB, AH, HD, AG, GC, BG, GD is a parallelogram, and their opposite sides are evidently equal. [I.34]
