Subsets and the canonical partition functions
  We explain the physical nature of the subset solution to the sign problem in chiral random matrix theory: The subset sum is shown to project out the canonical determinant with zero quark charge from a given configuration. As the grand canonical chiral random matrix partition function is independent of the chemical potential, the zero quark charge sector provides the full result. 
Jacques Bloch, Falk Bruckmann, Mario Kieburg, K. Splittorff and J. J.   M. Verbaarschot
hep-lat