### Matrix for z(5,5 | S_3 ∪ {O})

$I$ | $I$ | $I$ | $I$ | |

$I$ | $\alpha$ | $\alpha^2$ | $I$ | |

$\alpha$ | $I$ | $\alpha^2$ | $I$ | |

$\alpha^2$ | $I$ | $\alpha$ | $I$ | |

$\alpha^2$ | $\alpha$ | $I$ | $I$ |

Found by the quotient matrix algorithm. $I$ is the identity, $\alpha$ is a 3-cycle. The $I$ entries form an extremal rectangle-free matrix.

(838.845566686 seconds, score = 60, 9276201 recursive calls, max depth = 13)

Related: Matrix 299