Klein bottle group
= Klein bottle group
{c}
The fundamental group of the Klein bottle has presentation
$$
\langle a,b\mid aba^{-1}=b^{-1}\rangle.
$$
Its subgroup $\langle a^2,b\rangle\cong\mathbb Z^2$ has index two.
= Klein bottle group
{c}
The fundamental group of the Klein bottle has presentation
$$
\langle a,b\mid aba^{-1}=b^{-1}\rangle.
$$
Its subgroup $\langle a^2,b\rangle\cong\mathbb Z^2$ has index two.