The largest four-cycle-free 43 by 43 bipartite graph has between 284 and 299 edges; a new elementary argument rules out 300 edges.
Improvements for lower bounds of mutually orthogonal Latin squares of sizes $54$, $96$ and $108$
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abstract
We will show that there are at least 8, 10 and 9 mutually orthogonal Latin squares (MOLS) of orders $n=54$, $96$ and $108$. The cases $n=54$ and $96$ are obtained by constructing separable permutation codes consisting of $8 \times 54$ and $10 \times 96$ codeword respectively; in addition, these codes respectively have lengths $54$, $96$ and minimum distances $53$, $95$. Here we will follow exactly the procedure given in \cite{JS2019}. The case $n=108$ is obtained by constructing a $(108,10,1)$ difference matrix. Also, an error in \cite{ACD} for $n=45$ will be corrected.
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An Improved Upper Bound on the Zarankiewicz Number z(43;2)
The largest four-cycle-free 43 by 43 bipartite graph has between 284 and 299 edges; a new elementary argument rules out 300 edges.