Quaternions are not a field

They are "almost" a field, but in fact they are a division ring.
Saw mention of quaternions as a field in some of the comments.

No file, test, or entry point is named. Search the repository for references that call quaternions a field, then inspect the surrounding comments or documentation. Done means those references describe quaternions as a division ring rather than a field.

索引モデルが issue の本文から書いたものです。