makeEssential A
A central arrangement is essential if the intersection of all of the hyperplanes equals the origin. If ${\mathcal A}$ is a hyperplane arrangement in an affine space $V$ and $L$ is the intersection of all of the hyperplanes, then the image of the hyperplanes of ${\mathcal A}$ in $V/L$ gives an equivalent essential arrangement.
Since this essentialization is defined over a subring of the underlying ring of ${\mathcal A}$, it cannot be implemented directly. Instead, the method chooses a splitting of the quotient $V\to V/L$ and returns an arrangement over a polynomial ring on a subset of the original variables.
If ${\mathcal A}$ is already essential, then the method returns the same arrangement.
Deleting a hyperplane from an essential arrangement yields an essential arrangement only if the hyperplane was not a coloop.
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Type-$A$ reflection arrangements are not essential.
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Type-$B$ reflection arrangements are essential.
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