Limit Inferior/Examples/Sequence of Reciprocals

Example of Limit Inferior
Let $\sequence {a_n}$ be the sequence defined as:
 * $\forall n \in \N_{>0}: a_n = \dfrac 1 n$

The limit inferior of $\sequence {a_n}$ is given by:


 * $\displaystyle \map {\liminf_{n \mathop \to \infty} } {a_n} = 0$

Proof
From Sequence of Reciprocals is Null Sequence, $\sequence {a_n}$ is convergent:
 * $\displaystyle \lim_{n \mathop \to \infty} \dfrac 1 n = 0$

Let $L$ be the set of all real numbers which are the limit of some subsequence of $\sequence {a_n}$.

By Limit of Subsequence equals Limit of Real Sequence, all such subsequences have limit $0$.

Hence by definition of limit inferior:
 * $\displaystyle \map {\liminf_{n \mathop \to \infty} } {a_n} = \inf \set 0 = 0$