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Gupta S, Hill AV, Kwiatkowski D, Greenwood AM, Greenwood BM, Day KP.Gupta S, et al. Among authors: greenwood am, greenwood bm.Proc Natl Acad Sci U S A. 1994 Apr 26;91(9):3715-9. doi: 10.1073/pnas.91.9.3715.Proc Natl Acad Sci U S A. 1994.PMID: 8170975Free PMC article.