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The Sherrington-Kirkpatrick model couples every distinct pair of Ising spins using independent standard normal random variables $z_{ij}$ for $i<j$, with $J_{ji}=J_{ij}$. Here $J_0$ and $\mathcal{J}$ have units of energy. David Sherrington and Scott Kirkpatrick introduced this scaling in 1975; their original replica-symmetric calculation gave an unphysical negative low-temperature entropy. The model and that initial proposed solution must be distinguished.^[ref]