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Goel, Charu; Kuhlmann, Salma; Reznick, Bruce (May 2016). «On the Choi–Lam analogue of Hilbert's 1888 theorem for symmetric forms». Linear Algebra and Its Applications496: 114-120. arXiv:1505.08145. doi:10.1016/j.laa.2016.01.024.
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