  This is the third part of our series "Quasiclassical and Quantum Systems of
Angular Momentum". In two previous parts we have discussed the methods of group
algebras in formulation of quantum mechanics and certain quasiclassical
problems. Below we specify to the special case of the group ${\rm SU}(2)$ and
its quotient ${\rm SO}(3,\mathbb{R})$, and discuss just our main subject in
this series, i.e., angular momentum problems. To be more precise, this is the
purely ${\rm SU}(2)$-treatment, so formally this might also apply to isospin.
However. it is rather hard to imagine realistic quasiclassical isospin
problems.
