Hopping expansion as a tool for handling dual variables in lattice   models
  The hopping expansion of 8-vertex models in their Grassmann representation is studied. We use the functional similarity of the Ising model in this expansion with the hopping expansion of 2-D Wilson fermions to show that the lattice fermions are equivalent to the Self-avoiding Loop Model at bending rigidity 1/sqrt{2}. 
Christof Gattringer (MIT)