T H E E L E M E N T S	Book III   Proposition 30
	But equal straight lines cut off equal circumferences, the greater equal to the greater, and the less to the less; [III.28] and each of the circumferences AD, DB is less than a semicircle; therefore     the circumference AD is equal to the ciecumference DB. Therefore     The given circumference has been bisected at the point D. Being what it was required to do.
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