Definition

A smooth function (or C∞C^\infty-function), is a Cᵏ-function for all k∈ℤ+k \in \mathbb{Z}^+, i.e. an infinitely differentiable function


References

  1. http://staff.ustc.edu.cn/~wangzuoq/Courses/18F-Manifolds/Notes/Lec02.pdf