Show that the language $L = \{w \mid w \in \{a,b\}^{*}\}$ is not regular by using the following version of Pumping Lemma:
Let $L$ be the language, which has an infinite number of words, then there are words $x,y,z \in \Sigma ^{*}$, so that $|xz| \leq |\Sigma_{k}|$, and each word $xy^{(i)}z, i\geq 0$ is in $L$.
I don't really know how to use it. Could you give me a hint?