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On infinity type hyperplane arrangements and convex positive bijections

  • C. P. Anil Kumar

摘要

In this article we prove in main Theorem A that any infinity type real hyperplane arrangement \(\mathcal {H}_n^m\) H n m with the associated normal system \(\mathcal {N}\) N can be represented isomorphically by another infinity type hyperplane arrangement \(\widetilde{\mathcal {H}}_n^m\) H ~ n m with a given associated normal system \(\widetilde{\mathcal {N}}\) N ~ if and only if the normal systems \(\mathcal {N}\) N and \(\widetilde{\mathcal {N}}\) N ~ are isomorphic, that is, there is a convex positive bijection between a pair of associated sets of normal antipodal pairs of vectors of \(\mathcal {N}\) N and \(\widetilde{\mathcal {N}}\) N ~ . We show in Theorem 7.1 that, if two generic hyperplane arrangements \(\mathcal {H}_n^m\) H n m and \(\widetilde{\mathcal {H}}_n^m\) H ~ n m are isomorphic then their associated normal systems \(\mathcal {N}\) N and \(\widetilde{\mathcal {N}}\) N ~ are isomorphic. The converse need not hold, that is, if we have two generic hyperplane arrangements \((\mathcal {H}_n^m)_1\) ( H n m ) 1 , \((\mathcal {H}_n^m)_2\) ( H n m ) 2 in \(\mathbb {R}^m\) R m , whose associated normal systems \(\mathcal {N}_1\) N 1 and \(\mathcal {N}_2\) N 2 are isomorphic, then there need not exist translates of each of the hyperplanes in the hyperplane arrangement \((\mathcal {H}_n^m)_2\) ( H n m ) 2 , giving rise to a translated generic hyperplane arrangement \(\widetilde{\mathcal {H}}_n^m\) H ~ n m , such that, \(\widetilde{\mathcal {H}}_n^m\) H ~ n m and \((\mathcal {H}_n^m)_1\) ( H n m ) 1 are isomorphic.