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Bloom, Gary S. (1979), "A chronology of the Ringel–Kotzig conjecture and the continuing quest to call all trees graceful", Topics in Graph Theory (New York, 1977), Annals of the New York Academy of Sciences, vol. 328, New York: New York Academy of Sciences, pp. 32–51, doi:10.1111/j.1749-6632.1979.tb17766.x, MR0557885, S2CID84953734
