How to selectively use snippets from one filetype in another?

[medwatt]

I want to use my math snippets defined for latex in markdown. Instead of having one huge snippet file, I break them down into separate lua files and put them all in the same directory. For example, all my math snippets are defined inside $snippet_root/tex/math.lua. I want these snippets to be available for markdown. At the moment, if I include ls.filetype_extend("markdown", {"tex"}) in the snippet file definition for markdown, I get all the snippets from tex, not just those defined in math.lua. Is there a way to select extend markdown snippets with just math.lua and not the other files?