glue:math - Unknown Directive

[cuihantao]

Hi,

I hope you are having a great day. I tried the glue:math example from the documentation, and it doesn't work. Here's the code exactly from the doc:

import sympy as sym
f = sym.Function('f')
y = sym.Function('y')
n = sym.symbols(r'\alpha')
f = y(n)-2*y(n-1/sym.pi)-5*y(n-2)
glue("sym_eq", sym.rsolve(f,y(n),[1,4]))

  Insert the equation here:
  
  ```{glue:math} sym_eq
  :label: eq-sym
  ```
  
  Which we reference as Equation {eq}`eq-sym`

The error is shown below.

I checked that I have myst-nb version 1.3 installed. Let me know what else to check. Thank you!