"If a straight line be cut in extreme and mean ratio, the greater segment is also cut in extreme and mean ratio by the lesser segment."

"The prime numbers are more than any assigned multitude of prime numbers."

"And when the lines containing the angle are straight, the angle is called rectilineal."

"To construct a square on a given straight line."

"The postulates are not self-evident, but they are necessary for the development of geometry."