the unit disc的用法和样例：
例句
- In this question, all unnamed circles are unit circles.
在本题内，所以不命名的圆皆为单位圆。 - Classical complex variable method is followed, but a new conformal mapping formula is proposed so that the exterior part of the parabolic crack is mapped into a unit circle.
采用了传统的复变函数保角映射法，给出了一个新的保角变换公式，从而将抛物线曲裂纹外的区域映射到一个复平面的单位圆内。
