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On the k -Baire property

Alessandro Fedeli (1993)

Commentationes Mathematicae Universitatis Carolinae

In this note we show the following theorem: “Let X be an almost k -discrete space, where k is a regular cardinal. Then X is k + -Baire iff it is a k -Baire space and every point- k open cover 𝒰 of X such that card ( 𝒰 ) k is locally- k at a dense set of points.” For k = 0 we obtain a well-known characterization of Baire spaces. The case k = 1 is also discussed.

On the Lindelöf property of spaces of continuous functions over a Tychonoff space and its subspaces

Oleg Okunev (2009)

Commentationes Mathematicae Universitatis Carolinae

We study relations between the Lindelöf property in the spaces of continuous functions with the topology of pointwise convergence over a Tychonoff space and over its subspaces. We prove, in particular, the following: a) if C p ( X ) is Lindelöf, Y = X { p } , and the point p has countable character in Y , then C p ( Y ) is Lindelöf; b) if Y is a cozero subspace of a Tychonoff space X , then l ( C p ( Y ) ω ) l ( C p ( X ) ω ) and ext ( C p ( Y ) ω ) ext ( C p ( X ) ω ) .

On the n -fold symmetric product of a space with a σ - ( P ) -property c n -network ( c k -network)

Luong Q. Tuyen, Ong V. Tuyen (2020)

Commentationes Mathematicae Universitatis Carolinae

We study the relation between a space X satisfying certain generalized metric properties and its n -fold symmetric product n ( X ) satisfying the same properties. We prove that X has a σ - ( P ) -property c n -network if and only if so does n ( X ) . Moreover, if X is regular then X has a σ - ( P ) -property c k -network if and only if so does n ( X ) . By these results, we obtain that X is strict σ -space (strict -space) if and only if so is n ( X ) .

On the Noetherian type of topological spaces

S. A. Peregudov (1997)

Commentationes Mathematicae Universitatis Carolinae

The Noetherian type of topological spaces is introduced. Connections between the Noetherian type and other cardinal functions of topological spaces are obtained.

On the open-open game

Peg Daniels, Kenneth Kunen, Haoxuan Zhou (1994)

Fundamenta Mathematicae

We modify a game due to Berner and Juhász to get what we call “the open-open game (of length ω)”: a round consists of player I choosing a nonempty open subset of a space X and II choosing a nonempty open subset of I’s choice; I wins if the union of II’s open sets is dense in X, otherwise II wins. This game is of interest for ccc spaces. It can be translated into a game on partial orders (trees and Boolean algebras, for example). We present basic results and various conditions under which I or II...

On the paracompactness of frames

Xiangdong Chen (1992)

Commentationes Mathematicae Universitatis Carolinae

Through the study of frame congruences, new characterizations of the paracompactness of frames are obtained.

On the preservation of separation axioms in products

Milan Z. Grulović, Miloš S. Kurilić (1992)

Commentationes Mathematicae Universitatis Carolinae

We give sufficient and necessary conditions to be fulfilled by a filter Ψ and an ideal Λ in order that the Ψ -quotient space of the Λ -ideal product space preserves T k -properties ( k = 0 , 1 , 2 , 3 , 3 1 2 ) (“in the sense of the Łos theorem”). Tychonoff products, box products and ultraproducts appear as special cases of the general construction.

On the product of a compact space with an hereditarily absolutely countably compact space

Maddalena Bonanzinga (1997)

Commentationes Mathematicae Universitatis Carolinae

We show that the product of a compact, sequential T 2 space with an hereditarily absolutely countably compact T 3 space is hereditarily absolutely countably compact, and further that the product of a compact T 2 space of countable tightness with an hereditarily absolutely countably compact ω -bounded T 3 space is hereditarily absolutely countably compact.

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