Moduli spaces of coherent sheaves on multiple curves
sheaves, shtukas, and moduli; Impanga lecture notes", Trends in
Mathematics, Birkhäuser (2008).
In this paper we study coherent sheaves on reduced curves that
can be locally embedded in smooth surfaces. We define new invariants for these
sheaves : the generalized rank and degree, and prove a Riemann-Roch
theorem using them. The quasi locally free sheaves are natural
generalizations of locally free ones. We describe some moduli spaces of stable
such sheaves on double curves.