Tanım: $A\subseteq\mathbb{R}, \ f\in\mathbb{R}^A, \ a\in D(A)$ ve $L\in\mathbb{R}$ olmak üzere
$$\lim\limits_{x\to a}f(x)=L:\Leftrightarrow (\forall \epsilon >0)(\exists \delta >0)(\forall x\in A)(0<|x-a|<\delta\Rightarrow |f(x)-L|<\epsilon)$$
Teorem: $A\subseteq\mathbb{R}, \ f\in\mathbb{R}^A$ ve $a\in D(A)$ olmak üzere
$$(\forall L\in \mathbb{R})\left(\lim\limits_{x\to a}f(x)\neq L\right)\Leftrightarrow \left(\exists (x_n)\in (A\setminus \{a\})^{\mathbb{N}}\right)[x_n\to a \wedge \forall M(M\in \mathbb{R}\Rightarrow f(x_n)\nrightarrow M)]$$