"Self invertible" group Let there be an Abelian group with a binary operation $\ast$ on a set $S$. Let such a group respect the following propriety: $$ (X\ast Y)\ast Y = X$$ For any $X$ and $Y$ in $S$. I realize that by using the associative propriety we can say: $$ (X\ast Y)\ast Y = X \;\therefore\; X\ast (Y\ast Y) = X \;\therefore\; Y\ast Y = e$$ Where $e$ is the identity element of $\ast$, meaning that under $\ast$, any element of $S$ is it's own inverse. Could such a group exist? If so, what kind of proprieties would it have? Are there any examples? Much appreciated.

Yes, there are many groups where every element satisfies $Y * Y = e$. The simplest one is $\mathbb{Z}/2\mathbb{Z}$, the group of integers modulo 2 (under addition). These groups have interesting properties. For example you don't have to assume that the group is abelian; if a group is such that $Y * Y = e$ for all $Y$, it's automatically abelian.