《明史·志·卷八》
勾股内又形成小勾股，就有小勾、小股、小弦，而大小可以互相推求，平侧可以互相利用，圆周的道理，这就很切近了。
句股内成小句股，则有小句、小股、小弦、而大小可互求，平侧可互用，浑圆之理，斯为密近。
Another Pythagorean triangle is formed within the Pythagorean triangle, with a small perpendiculator, a small base, and a small hypotenuse, and the large and small components can each be deduced from the other, and the side and the hypotenuse can each be used to produce the other, which is a very close approximation of the principles of a circumference.