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1.64 (1965)

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A torsion-free group is said to be separable if it can be represented as the set-theoretic union of two of its proper subsemigroups. Is every $R$-group separable?

Contributor: P. G. Kontorovich

Progress

No (S. J. Pride, J. Wiegold, Bull. London Math. Soc., 9 (1977), 36–37).

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