R2Z2, what a strange pseudonym which obviously reminds of a droid from a science fiction hexalogy but which does not have it roots in it.
Actually, this user name comes from the mathematical notation refering by definition to the set which happens to have the topology of a torus surface.
![{\displaystyle \{\{(x,y)\in \mathbb {R} ^{2}/x\equiv a[1]~et~y\equiv b[1]\}/(a,b)\in \mathbb {R} ^{2}\}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/595c6bad6db3d02046a6da750f9c66fd7b11ab53)
