初等函数#

函数极限的定义#

邻域#

邻域$U(x_{0})$ 去心邻域$\mathring{U}(x_{0})$$\delta$领域：$x_{0} \quad \delta>0\quad(x_{0}-\delta,x_{0}+\delta)\quad \text{记作}U(x_{0},\delta)$$\delta$去心邻域：$x_{0} \quad \delta>0\quad(x_{0}-\delta,x_{0})\cup(x_{0,}x_{0}+\delta)\quad \text{记作}\mathring{U}(x_{0},\delta)$