T H E E L E M E N T S	Book VI   Proposition 4
	Now,     since the angle DCE is equal to the angle ABC     BF is parallel to CD. [I.28] Again,     since the angle ACB is equal to the angle DEC     AC is parallel to FE. [I.28] Therefore     FACD is a parallelogram; therefore     FA is equal to DC, and AC to FD. [I.34]
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