Let $\Gamma$ be a connected finite Dynkin diagram of rank $\ell$, with generalized Cartan matrix $A = (a_{ij})_{1 \leq i,j \leq \ell}$. For distinct vertices $i$ and $j$, define the bond multiplicity between $i$ and $j$ to be
Then every multiple bond in $\Gamma$ has multiplicity $2$ or $3$. If $\Gamma$ contains a triple bond, then $\ell = 2$ and $\Gamma$ is of type $G_2$. If $\Gamma$ contains a double bond and $\ell \geq 3$, then $\Gamma$ is one of the types $B_\ell$, $C_\ell$, or $F_4$.