The deletion double-point conjecture for free line arrangements

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Let A{\mathcal A} be a free projective line arrangement in PK2{\mathbf P}^2_{\mathbb K}, where K{\mathbb K} is a field of characteristic zero. Let H∈AH\in {\mathcal A}, and write n2(A∖{H})n_2({\mathcal A}\setminus\{H\}) for the number of double points of the deleted arrangement.

Deletion double-point conjecture. If A∖{H}{\mathcal A}\setminus\{H\} is not free, then

n2(A∖{H})>0.n_2({\mathcal A}\setminus\{H\})>0.

The source presents this as a weaker version of the preceding nonfree line-arrangement conjecture. No resolution is supplied in the given text.

References

Primary source

Takuro Abe, “Double points of free projective line arrangements”, arXiv:1911.10754 (2019).

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