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Restricted completion of sparse partial Latin squares

  • Lina J. Andrén (a1), Carl Johan Casselgren (a2) and Klas Markström (a3)

Abstract

An n × n partial Latin square P is called α-dense if each row and column has at most αn non-empty cells and each symbol occurs at most αn times in P. An n × n array A where each cell contains a subset of {1,…, n} is a (βn, βn, βn)-array if each symbol occurs at most βn times in each row and column and each cell contains a set of size at most βn. Combining the notions of completing partial Latin squares and avoiding arrays, we prove that there are constants α, β > 0 such that, for every positive integer n, if P is an α-dense n × n partial Latin square, A is an n × n (βn, βn, βn)-array, and no cell of P contains a symbol that appears in the corresponding cell of A, then there is a completion of P that avoids A; that is, there is a Latin square L that agrees with P on every non-empty cell of P, and, for each i, j satisfying 1 ≤ i, jn, the symbol in position (i, j) in L does not appear in the corresponding cell of A.

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Corresponding author

*Corresponding author. Email: carl.johan.casselgren@liu.se

Footnotes

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Part of the work done while the author was a postdoctoral researcher at the Mittag-Leffler Institute. Research supported by a postdoctoral grant from the Mittag-Leffler Institute.

Part of the work done while the author was a postdoctoral researcher at the Mittag-Leffler Institute. Research supported by a postdoctoral grant from the Mittag-Leffler Institute.

§

Part of the work done while the author was visiting the Mittag-Leffler Institute. Research supported by the Mittag-Leffler Institute.

Footnotes

References

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