On generalization of theorems of Pestryakov (Q2215696)

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On generalization of theorems of Pestryakov
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    On generalization of theorems of Pestryakov (English)
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    14 December 2020
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    Fix a Tychonoff space \((X,\tau)\). Denote by \(X_{\aleph_0}\) the set \(X\) endowed with the Baire topology, i.e. the topology having as a basis the family \(Z(X)\) of all zero sets of continuous real-valued functions on \(X\). Set \(L(X)=\{\sum_{i=1}^kn_i\chi_{Z_i}\mid Z_i\in Z(X), k,i,n_i\in\mathbb N\}\), where \(\chi_S\) denotes the characteristic function on \(S\). Define \(\mathbb B(X)=\{Y \mid L(X)\subset Y\subset C(X_{\aleph_0})\}\). Extending results of \textit{A. V. Pestryakov} [in: Investigations on the theory of convex sets and graphs. Collection of scientific works. Sverdlovsk: Ural'skiĭ Nauchnyĭ Tsentr AN SSSR. 53--59 (1987; Zbl 0662.54001)] the author relates cardinalities, such as tightness, hereditary density, hereditary Lindelöfness, spread, pseudocharacter, network weight and the Lindelöf number of \(\mathbb B(X)\) to cardinalities of \(X\) or \(X_{\aleph_0}\).
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    space of Baire functions
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    density
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    tightness
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    Lindelöf number
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    spread
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    \( G_\delta \)-modification
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    selection principles
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    cardinal functions
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