On the set of continuously differentiable concave extensions of a Boolean function
Vestnik rossijskih universitetov. Matematika, Tome 30 (2025) no. 149, pp. 5-14

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This paper is devoted to the study of the existence of extremal elements of the set of continuously differentiable concave extensions to the set $[0,1]^n$ of an arbitrary Boolean function $f_{B}(x_1,\ldots,x_n)$, as well as finding the cardinality of the set of continuously differentiable concave extensions to $[0,1]^n$ of the Boolean function $f_{B}(x_1,\ldots,x_n).$ As a result of the study, it is proved that, firstly, for any Boolean function $f_{B}(x_1,\ldots,x_n)$ among its continuously differentiable concave extensions to $[0,1]^n$ there is no maximal element, secondly, if the Boolean function $f_{B}(x_1,\ldots,x_n)$ has more than one essential variable, then among its continuously differentiable concave extensions to $[0,1]^n$ there is no minimal element, and if the Boolean function is constant or has only one essential variable, then among its continuously differentiable concave extensions to $[0,1]^n$ there is a unique minimal element, the explicit form of which is given in the paper. It was also established that the cardinality of the set of continuously differentiable concave extensions to $[0,1]^n$ of an arbitrary Boolean function $f_{B}(x_1,\ldots,x_n)$ is equal to the continuum.
Keywords: continuously differentiable concave extension of a Boolean function, extremal elements of a set, cardinality of a set
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     title = {On the set of continuously differentiable concave extensions of a {Boolean} function},
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D. N. Barotov; R. N. Barotov. On the set of continuously differentiable concave extensions of a Boolean function. Vestnik rossijskih universitetov. Matematika, Tome 30 (2025) no. 149, pp. 5-14. http://geodesic.mathdoc.fr/item/VTAMU_2025_30_149_a0/