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Restricted completion of sparse partial Latin squares.
Combinatorics, Probability and Computing, 1-21. doi:10.1017/S096354831800055X, Cambridge University Press. Abstract An n × n partial Latin square P is called α-dense if each row and column has at most αnnon-emp times in . An × array where each cell contains a subset of {1,…, } is a (, ) -array if each symbol occurs at most times in each row and column and each cell contains a set of size at most . Combining the notions of completing partial Latin squares and avoiding arrays, we prove that there are constants , > 0 such that, for every positive integer , if is an -dense × partial Latin square, is an × -array, and no cell of contains a symbol that appears in the corresponding cell of , then there is a completion of that avoids ; that is, there is a Latin square that agrees with on every non-empty cell of , and, for each , satisfying 1 ≤ , ≤ , the symbol in position (, ) in does not appear in the corresponding cell of .
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