substitution definition of a math formula

Dzhelil Rufat created an issue

It seems to be impossible to define substitutions for math formulas.

To demonstrate the error, try to compile the following simple code

This is a simple math equation |eqn| .

.. |eqn|  math:: e^{i\pi} + 1 = 0


When I try to compile it, am getting the following error:

(WARNING/2) Substitution definition "eqn" empty or invalid.

.. |eqn|  math:: e^{i\pi} + 1 = 0



.. |eqn| replace:: :math:formula