Introduction

Abstract

Let V be a vector space of dimension ℓ ≥ 1 over the field K. An arrangement A = {H₁, …, H_n} is a set of n ≥ 0 hyperplanes in V . In dimension 1, we consider n points in the real line ℝ or in the complex line ℂ. We shall see later that these seemingly innocent examples lead to interesting problems. In dimension 2, the Selberg arrangement of five lines is shown below. We shall use this arrangement to illustrate definitions and results in Section 1.11.