Symplectic models of groups with noncommutative spaces Zakrzewski, S. — 1993 Proceedings of the Winter School "Geometry and Topology"
Poisson structures on ℝ 2 N having only two symplectic leaves: the origin and the rest S. Zakrzewski — 2000 Banach Center Publications Examples of Poisson structures with isolated non-symplectic points are constructed from classical r-matrices.
Quantum deformations of the Lorentz group. The Hopf-algebra level S. L. Woronowicz; S. Zakrzewski — 1994 Compositio Mathematica