1. A class of torsion-free abelian groups of finite rank;Butler,1965
2. Warfield modules;Hunter,1981
3. Nice subgroups of valuated group;Moore,1981
4. Modules over a complete discrete valuation ring;Rotman;Trans. Amer. Math. Soc.,1961
5. An invariant for modules over a discrete valuation ring;Stanton,1975