where, as before, the product ${\prod}^{n}$ is over all the $\beta_{\ell,u}$ for transitions through *negative* elementary moves along the *reverse sequence* $\psi$ leaving the energy unchanged, and the product ${\prod}^{nn}$ is over all $\gamma_{\ell,u}$ where the transition is a *negative* elementary move along the *reverse sequence* $\psi$ decreasing the energy.

For example, consider the model of collapsing walks in figure \[figure3\] and suppose the sequence $\phi$ is realised, where

at -25 5 at 0 0 at 20 0 40 0 50 0 / at 40 0 50 0 / at 70 0 90 0 100 0 100 10 / at 90 0 100 0 100 10 / at 120 0 140 0 150 0 150 10 140 10 / at 140 0 150 0 150 10 140 10 / at 170 0 190 0 200 0 200 10 / at 190 0 200 0 200 10 / at 220 0 240 0 250 0 250 10 240 10 / at 240 0 250 0 250 10 240 10 / at 270 0 300 0 310 0 310 10 300 10 290 10 / at 300 0 310 0 310 10 300 10 290 10 / at 320 5 at 0 