The ideal of definition of a linear subspace in a projective space has a very simple structure and hence a very simple free resolution, i.e. a Koszul complex. What can we say for the ideal that defines a finite collection of linear subspaces, subspace arrangements, in a projective space? Here we can take the intersection of the ideals defining the individual subspaces or their product. For the intersection, the structure of the resolution remains largely mysterious. For the product instead the resolution can be described and it turns out that it is supported on a polymatroid associated with the subspace arrangement. Joint work with Manolis Tsakiris (Chinese Academy of Sciences). arXiv:1910.01955v2