 the $Z(\cH_0(\bfq))$-algebra $\operatorname{End}_{Z(\cH_0(\bfq))}(\cA_0(\bfq))$ of $Z(\cH_0(\bfq))$-linear endomorphisms of $\cA_0(\bfq)$. Recall that $Z(\cH_0(\bfq))= \cA_0(\bfq)^s$ is the subring of invariants of the commutative ring $\cA_0(\bfq)$.  