Prove that the fundamental group of a Klein bottle is $\displaystyle G = \{ a^{m}b^{2n+\epsilon} \ ;\ m \in \mathbb{Z}, \ n \in \mathbb{Z} \ \epsilon = 0 \ or\ 1, \ ba=a^{-1}b\}$, i.e. G is the group on two generators $\displaystyle a ,\ b$ with one relation $\displaystyle ba=a^{-1}b$