Erdős–Ko–Rado and Hilton–Milner theorems for two-forms

Abstract

The celebrated Erdős–Ko–Rado theorem about the maximal size of an intersecting family of r-element subsets of {1,…,n} was extended to the setting of exterior algebra in [5, Theorem 2.3] and in [6, Theorem 1.4]. However, the equality case has not been settled yet. In this short note, we show that the extension of the Erdős–Ko–Rado theorem and the characterization of the equality case therein, as well as those of the Hilton–Milner theorem to the setting of exterior algebra in the simplest non-trivial case of two-forms follow from a folklore puzzle about possible arrangements of an intersecting family of lines.