
arXiv: 1901.09814
For a family $A\subseteq\left\{ 0,\dots,k\right\} ^{n}$, define the $\delta$-shadow of $A$ to be the set obtained from $A$ by removing from any of its vectors one coordinate that equals zero. Given the size of $A$, how should we choose $A$ to minimise its $\delta$-shadow? Our aim in this paper is to show that, for any $r$, the family of all sequences with at most $r$ zeros has minimal $\delta$-shadow. We actually give the exact best $A$ for every size.
Extremal set theory, FOS: Mathematics, Mathematics - Combinatorics, Kruskal-Katona theorem, Combinatorics (math.CO), lower shadow
Extremal set theory, FOS: Mathematics, Mathematics - Combinatorics, Kruskal-Katona theorem, Combinatorics (math.CO), lower shadow
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