What would be a good (as "easy" as possible) example of a Triangular (Non trivial) quasi-Hopf algebra? By trivial I mean the quasi strcture not to be trivial, but if the triangular structure is trivial it's ok (it's actally better for me) 
Setting $c:=b^{-1}$ one obtains the presentation
$$G= \langle a,c \,  | \, a^2c^2=1 \rangle,$$
which is the fundamental group of the Klein bottle.

It is well known that another presentation of such a group is 
$$G= \langle x,y \,|\, x^{-1}yx=y^{-1} \rangle,$$
and this allows one to write $G$ as a semi-direct product of infinite cyclic groups, namely $$G= \mathbb{Z} \rtimes_{\sigma} \mathbb{Z}$$
where $\sigma \colon \mathbb{Z} \to \mathbb{Z}$ is defined by $\sigma(y)=y^{-1}$ and $\mathbb{Z}$ is written multiplicatively.
