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JOURNALS // Sibirskii Matematicheskii Zhurnal // Archive

Sibirsk. Mat. Zh., 2015 Volume 56, Number 2, Pages 368–376 (Mi smj2643)

Some generalization of the Arkhangel'skiĭ–Kombarov theorem for seminormal functors

A. V. Ivanov

Petrozavodsk State University, Faculty of Mathematics, Petrozavodsk, Russia

Abstract: We introduce the notion of variative seminormal functor $\mathscr F$ and prove that, for each of these functors and every compact space $X$, the normality of the space $\mathscr F(X)\setminus X$ is countable. Thus, we obtain a generalization of the Arkhangel'skiĭ–Kombarov theorem of 1990 on the countability of the character of a compact space which is normal outside the diagonal. Under the assumption of Jensen's principle, we prove that the above assertion fails for finite nonvariative functors.

Keywords: seminormal functor, Arkhangelskiĭ–Kombarov theorem, first-countability, normality outside the diagonal.

UDC: 515.12

Received: 16.11.2013


 English version:
Siberian Mathematical Journal, 2015, 56:2, 297–303

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© Steklov Math. Inst. of RAS, 2025