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Quotation from Elements, Books I-VI by Euclid
“In a circle—(1). The angle in a semicircle is a right angle”
Elements, Books I-VI, Book III, Proposition XXXI, trans. John Casey (3rd ed., 1885)
The first part of III.31, a result traditionally associated with Thales.
Citation: "In a circle—(1). The angle in a semicircle is a right angle" — Euclid, Elements, Books I-VI, Book III, Proposition XXXI, trans. John Casey (3rd ed., 1885). (id euclid-elements-books-i-vi-q6)
