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\prod_{i=m}^{z} p_{\rm trial}^{\rm arb}({\bf r}_i) \times
\prod_{i=m}^{z} P_{\rm select}({\bf r}_i) \times
P_{\rm accept} ({\bf r}_m, ..., {\bf r}_z)
=
\left(\prod_{i=m}^{z} p_{\rm trial}^{\rm ideal}({\bf r}_i)\right) \exp\left[-\beta u({\bf r}_m, ..., {\bf r}_z)\right]
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