  The algebraic consistency of spin and isospin at the level of an unbroken
SU(2) gauge theory suggests the existence of an additional angular momentum
besides the spin and isospin and also produces a full quaternionic spinor
operator. The latter corresponds to a vector boson in space-time, interpreted
as a SU(2) gauge field. The existence of quaternionic spinor fields implies in
a quaternionic Hilbert space and its necessary mathematical analysis. It is
shown how to obtain a unique representation of a quaternion function by a
convergent positive power series.
