These are also called the planar quaternions and are the even subalgebra of 2D PGA. I use and explain these (and their nD generalisations) in my SIBGRAPI 2021 t

These are also called the planar quaternions and are the even subalgebra of 2D PGA. I use and explain these (and their nD generalisations) in my SIBGRAPI 2021 talk on kinematics and dynamics in PGA. https://youtu.be/pq9YfdPHhIo https://youtu.be/pq9YfdPHhIo There is also a writeup called 'may the forque be with you' available on bivector.net