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Published online by Cambridge University Press: 26 February 2010
Professor Kneser has pointed out to me that the results proved in my paper [3] are not new. To be precise, my Theorem 1 is a special case of the result proved in [2], while the routine argument by which I deduced my Theorem 2 is given in substance in [1; 241]. Then my Theorem 3, though perhaps new, follows almost trivially.