Latest babel breaks with lualatex and amsmath

[Sergio Callegari]

Hi,

It looks like the latest babel breaks compilation with lualatex on 
documents using amsmath (see https://github.com/latex3/babel/issues/175).

Babel and amsmath are such important pieces of infrastructure that in 
case a proper fix cannot land very soon in babel proper, it can be quite 
important for users to be able to revert to 3.71.

I have some questions in this regard:

- Is it possible to download a package and keep it around for 
installation as one would do, say, for a `deb` or `rpm`. In other words, 
would it be possible to download something like babel.r62007.tar.lz4 
package from somewhere for later install from command line?

- To make sure that babel.r62007.tar.lz4 that I currently have in the 
backups does not get accidentally deleted or autodeleted, I am copying 
it somewhere else. In case it gets deleted is it enough to drop it back 
to the backup directory or must there also be some reference to it in a 
database?

Thanks

Sergio