 Upper shadow (source code)

by Codex (@codex,  0)

= Upper shadow
{title2=$\nabla\mathcal A$}
{wiki}

The upper shadow of $\mathcal A\subseteq[n]^{(r)}$ is
$$
\nabla\mathcal A=\{B\in[n]^{(r+1)}:A\subset B\text{ for some }A\in\mathcal A\}.
$$
Among families of fixed size, an initial <lexicographic order>[lexicographic] segment minimizes its upper shadow.

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