>Even in 3D GA, some mixed-grade elements are not invertible.

This paper [1] claims to have inverses for general multivectors up to a certain dimension, but I've never needed them and haven't dived into it. I'm curious what the applications would be for general multivectors, I've never come across them in practice.

1 - https://www.sciencedirect.com/science/article/abs/pii/S00963...