Formula_24630

\[\begin{gathered}U^{\prime}\left(\sigma_{x_{1}}, \ldots, \sigma_{x_{V}}\right)=-\sum_{X \subset \Lambda} J_{X} \sigma^{X}, \\Z=\sum_{\sigma} \exp \left[-U^{\prime}\left(\sigma_{x_{1}}, \ldots, \sigma_{x_{V}}\right)\right]\end{gathered}\]