Addition-Deletion Theorems for Factorizations of Orlik-Solomon Algebras and nice Arrangements

We study the notion of a nice partition or factorization of a hyperplane arrangement due to Terao from the early 1990s. The principal aim of this note is an analogue of Terao's celebrated addition-deletion theorem for free arrangements for the class of nice arrangements. This is a natural setting for the stronger property of an inductive factorization of a hyperplane arrangement by Jambu and Paris. In addition, we show that supersolvable arrangements are inductively factored and that inductively factored arrangements are inductively free. Combined with our addition-deletion theorem this leads to the concept of an induction table for inductive factorizations. Finally, we prove that the notions of factored and inductively factored arrangements are compatible with the product construction for arrangements.Comment: 24 pages; v2 26 pages: added new example over complex numbers of an inductively free and factored arrangement which is not inductively factored, added comment on proper containment of hereditary factored classes; v3 final version, small changes as suggested by referees; to appear in European. J. Com

Combinatorics and freeness of hyperplane arrangements and reflection arrangements

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