Topology
《Topology》 · 第 213 页 · Chapter 9，Section 9.28
The crystal graph of a crystal base $(\mathcal{L}, B)$ is a coloured directed graph with set of vertices $B$ and with set of types equal to $\Pi$. If $b$ and $b'$ are vertices, then there is an arrow of type $\alpha$ from $b$ to $b'$ if and only if $b' = \tilde{F}_\alpha b$.