  For an abelian or a projective K3 surface $X$ over an algebraically closed
field $k$, consider the moduli space $\splcpx_{X/k}\uet$ of the objects $E$ in
$D^b(\mathrm{Coh}(X))$ satisfying $\Ext^{-1}_X(E,E)=0$ and $\Hom(E,E)\cong k$.
Then we can prove that $\splcpx_{X/k}\uet$ is smooth and has a symplectic
structure.
