A **($U_q(\mathfrak{g})$-)crystal** is a nonempty set $B$ together with maps
\[
\begin{aligned}
&\mathrm{wt}: B \to P\\
&e_i, f_i : B \to B \cup \{0\} \quad \text{for all } i\in I.
\end{aligned}
\]
Here $\mathfrak{g}$ is a Lie or Kac-Moody algebra of a particular type with index set $I$.

The map $\mathrm{wt}$ is called the weight function which maps a crystal element to a weight in the weight lattice $P$. The maps $e_i$ and $f_i$ are called Kashiwara raising and lowering operators.

**Authors:**

**Knowl status:**

- Review status: beta
- Last edited by Alex J. Best on 2018-12-13 13:45:10

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