This symbol represents a unary function. Its argument is a
ring R. When evaluated on R, the function represents the
ring of quaternions over R, that is, the ring with basis
1,i,j,k over R such that ij=-ji=k, i^2=j^2=k^2=-1.
Commented Mathematical property (CMP):
The quaternion ring over R is isomorphic to the quotient of the free ring over
R generated by i, j, k subject to the relations
ij=-ji=k and i^2=j^2=k^2=-1.