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https://doi.org/10.1007/s10958-020-04903-0 (Publisher version)
https://www.mathnet.ru/eng/fpm/v21/i5/p219 (Publisher version)
Troitsky, E. V. (2020). Two examples related to the twisted Burnside-Frobenius theory for infinitely generated groups. Journal of Mathematical Sciences, 248(5), 661-666. doi:10.1007/s10958-020-04903-0.