Central extensions of cotangent universal hierarchy: (2+1)-dimensional   bi-Hamiltonian systems
  We introduce the cotangent universal hierarchy that extends the so-called universal hierarchy (as for the latter, see e.g. arXiv:nlin/0202008, arXiv:nlin/0312043 and arXiv:nlin/0310036). Then we construct a (2+1)-dimensional double central extension of the cotangent universal hierarchy and show that this extension is bi-Hamiltonian. This yields, as a byproduct, the central extension of the original universal hierarchy. 
Artur Sergyeyev and Blazej M. Szablikowski