Hi @andreas.dorta , welcome to the neo4j community.
Could you elaborate on the kind of problems that you're having when trying to import the FMA ontology? It's not particularly big (2.7 million triples). I've run it on my laptop and the import process took just over 30 seconds.
Depending on your hw setup it may take a bit longer but I see no particular issue with it.
Here's a screen capture of a small bit of the class hierarchy (subclassof), with some object properties ( along with their domain, range, etc.)
This approach imports every single triple in the FMA ontology into Neo4j but you'll find that things like the constraint definitions (owl:constraint) are loaded in a rather awkward way making them sometimes not very easy to use. Although this will depend on your use case, of course.
You may find this conversation on that topic useful:
Could you share a bit more of what your'e trying to achieve? What do you mean by "mathematical descriptions"?
Regards,
JB.