  It is an easily deduced fact that any four-component spin 1/2 state for a
massive particle is a linear combination of pairs of two-component simultaneous
rotation eigenstates, where `simultaneous' means the eigenspinors of a given
pair share the same eigenvalue. The new work here constructs the reverse: Given
pairs of simultaneous rotation eigenvectors, the properties of these pairs
contains relationships that are equivalent to spin 1/2 single particle
equations. Thus the needed aspects of space-time symmetry can be produced as
special cases of more general properties already present in the rotation group.
The exercise exploits the flexibility of the rotation group in three dimensions
to deduce relativistic quantities in four dimensions.
