  We review a recently proposed approach to the problem of alternating signs
for fermionic many body Monte Carlo simulations in finite temperature
simulations. We derive an estimate for fermion wandering lengths and introduce
the notion of permutation zones, special regions of the lattice where identical
fermions may interchange and outside of which they may not. Using successively
larger permutation zones, one can extrapolate to obtain thermodynamic
observables in regimes where direct simulation is impossible.
