Let A be an arrangement of n open halfspaces in R. In [2], Linhart proved that for r â‰¤ 5, the numbers of vertices ofA contained in at most k halfspaces are bounded from above by the correspondingâ€¦ (More)

We characterize skew-symmetric {1; 0;âˆ’1}-matrices with a certain combinatorial property. In particular, we exhibit several equivalent descriptions of this property. These results allowâ€¦ (More)