When trying to start retext on clean config, it immediately crashes with the following stack-trace:

Traceback (most recent call last):
File "/usr/bin/retext", line 111, in <module>
main()
File "/usr/bin/retext", line 79, in main
window = ReTextWindow()
File "/usr/lib/python3.6/site-packages/ReText/window.py", line 217, in __init__
availableMarkups = markups.get_available_markups()
File "/usr/lib/python3.6/site-packages/markups/__init__.py", line 33, in get_available_markups
for markup in get_all_markups():
File "/usr/lib/python3.6/site-packages/markups/__init__.py", line 23, in get_all_markups
return [entry_point.load() for entry_point in entry_points]
File "/usr/lib/python3.6/site-packages/markups/__init__.py", line 23, in <listcomp>
return [entry_point.load() for entry_point in entry_points]
File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2317, in load
self.require(*args, **kwargs)
File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2340, in require
items = working_set.resolve(reqs, env, installer, extras=self.extras)
File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 774, in resolve
raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'python-markdown-math' distribution was not found and is required by the application

python-markdown-math[1] is available in AUR and fix the issue.

Additional info:
* retext 7.0.1-1

Steps to reproduce:
- Install retext from 'community'
- Try starting it

[1] https://aur.archlinux.org/packages/python-markdown-math/