1. Embedding theorems for abelian groups with valuations;Conrad, Paul F.;Amer. J. Math.,1953
2. Extensions of ordered groups;Conrad, Paul;Proc. Amer. Math. Soc.,1955
3. A. G. Kurosh, The theory of groups, Chelsea, New York.
4. Ordered groups;Levi, F. W.;Proc. Indian Acad. Sci., Sect. A.,1942