@duerer about those two videos on your to-watch list: the first one (Numberphile) is great, but I’d avoid the second one if I were you (haven’t seen that one, so…); that’s a 4d hypersphere one that will probably just confuse you and saying in the title that a quaternion is a 4d number is complete and utter nonsense: there are no 4d numbers. Numbers have dimension 0 when they have a dimension at all. Like a point in 3D space; the point is not a 3 dimensional point! It is a point in 3D space!
