Semigroups which admit few embeddings
Kenneth Magill (1974)
Fundamenta Mathematicae
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Kenneth Magill (1974)
Fundamenta Mathematicae
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Magill, K. D., Jr.
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Kenneth D., Jr. Magill, Prabudh Ram Misra, U. B. Tewari (1983)
Czechoslovak Mathematical Journal
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Zdeněk Frolík (1960)
Czechoslovak Mathematical Journal
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A. Nagy (1986-1987)
Semigroup forum
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Ofelia Teresa Alas, Mihail G. Tkachenko, Vladimir Vladimirovich Tkachuk, Richard Gordon Wilson, Ivan V. Yashchenko (2001)
Czechoslovak Mathematical Journal
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We prove that it is independent of ZFC whether every Hausdorff countable space of weight less than has a dense regular subspace. Examples are given of countable Hausdorff spaces of weight which do not have dense Urysohn subspaces. We also construct an example of a countable Urysohn space, which has no dense completely Hausdorff subspace. On the other hand, we establish that every Hausdorff space of -weight less than has a dense completely Hausdorff (and hence Urysohn) subspace....