Let $\Phi$ be a set of bijections $\phi\_a:X\to Y$. To each pair of bijections $\phi\_a$, $\phi\_b$ one naturally relates a bijection $\psi\_{ab}:=\phi\_a^{-1}\circ\phi\_b: X\to X$. In some cases the set of all such $\psi\_{ab}$ forms a subgroup of $Sym(X)$, the group of all bijections $X\to X$.


Were these kinds of constructions studied in any generality? The question arose as in our very special setting, with $X$ finite, the resulting group turned out to be abelian. At least it would be nice to know if this kind of construction has a name. 



a group from a family of bijections X->Y
The name you are looking for is that of a **torsor** or **principal homogeneous space**. For any sets $X$ and $Y$, the set of bijections $X \to Y$ is a torsor for the group $\mathrm{Sym}(X)$ acting on the right as well as the group $\mathrm{Sym}(Y)$ acting on the left. In your case, the set $\Phi$ is a torsor for the abelian group you constructed.


