The complete nontrivial-intersection theorem for vector spaces

Abstract

A family of $k$-subspaces of an $n$-dimensional vector space over a finite field is $t$-intersecting if any two members intersect in a subspace of dimension at least $t$. A $t$-intersecting family is nontrivial if no $t$-subspace is contained in all its members. In this paper, we determine the largest nontrivial $t$-intersecting families for $k\ge t+2$ and $n\ge 2k+1$. As a result, the complete nontrivial-intersection theorem for vector spaces is established.