# Closure relations between Bruhat cells on the flag variety

Given a Lie group $G$ over $\mathbb{C}$ and a Borel subgroup $B$. There is this famous Bruhat decomposition of the flag variety $G/B$.

How do we prove the closure relations between the cells, which are indexed by the Weyl group elements?

I was thinking about constructing a curve that connects two $T-$fixed points, using the exponential map. Let $e_{\alpha}$ be a root in the Lie algebra. How do we think about the action of $\exp(t \cdot e_{\alpha})$ on $G/B$, as $t \rightarrow \infty$?

The place I've read about this is in the paper "Schubert cells, and the cohomology of the spaces $G/P$" by Berstein, Gelfand, and Gelfand. The flag variety can be identified with the projectivization of a representation of $G$, $V_{\lambda}$. Then you compute the limit of the 1-psg $exp(t\cdot e_{\alpha})$ as it acts on weight vector $v_{w\lambda}$. As $t\to \infty$, you get $v_{s_{\alpha}w\lambda}$.