ZarankiewiczDB,

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Matrix for z(4,4 | 4,4)

$I$$I$$I$$\alpha$
$I$$\beta$$\alpha\beta$$I$
$\alpha\beta$$I$$\beta$$I$
$\beta$$\alpha\beta$$I$$I$

$I$ is the identity, and $\alpha,\beta$ generate $\mathbb{Z}_2 \times \mathbb{Z}_2$. The $I$ entries form an extremal rectangle-free matrix, showing that the finite projective plane of order 4 is sub-similar.

weight = 64, submitted by Andrew Kay on April 22nd, 2016 (link, raw)