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2. English translation: J. Math. Sci., 207, No. 1, 26-38 (2015), https://doi.org/10.1007/s10958-015-2352-2
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5. English translation: Ukr. Math. J., 66, No. 2, 232-241 (2014), https://doi.org/10.1007/s11253-014-0925-8