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Not all free arrangements are K(π,1)

Paul H. Edelman, Victor Reiner

math.ATarXiv:math/9501229

Abstract

We produce a one-parameter family of hyperplane arrangements that are counterexamples to the conjecture of Saito that the complexified complement of a free arrangement is K(π,1). These arrangements are the restriction of a one-parameter family of arrangements that arose in the study of tilings of certain centrally symmetric octagons. This other family is discussed as well.

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