  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.
