Virasoro Symmetry Algebra of Dirac Soliton Hierarchy
  A hierarchy of first-degree time-dependent symmetries is proposed for Dirac soliton hierarchy and their commutator relations with time-dependent symmetries are exhibited. Meantime, a hereditary structure of Dirac soliton hierarchy is elucidated and a Lax operator algebra associated with Virasoro symmetry algebra is given. 
Wen-Xiu Ma and Kam-Shun Li