1. Show that is not isomorphic to .
2. Show that no two of are isomorphic,
3. Show that \ is a group under multiplication. H is quaternion algebra.
1. The set of rational number is commutative, but is not, so would that be the reason?
2. I want to say that T contains element with the order 6 while does not, would that be right?
3. For this one I'm just simply lost, would anyone please explain more what H is?