刚性理论是子流形几何中久盛不衰的重要方向，其根源可追溯到经典曲面论的高斯绝妙定理。
Rigidity theory is one ever-flourishing subject in geometry of submanifolds , which can be traced back to Gauss ' Theorema Egregium in the classical theory of surfaces .
高斯绝妙定理