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Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 38, No. 3, pp. 309–314, May–June, 1986.
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Gorbaichuk, V.I. Inverse theorems for approximation by harmonic functions. Ukr Math J 38, 266–271 (1986). https://doi.org/10.1007/BF01056821
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DOI: https://doi.org/10.1007/BF01056821