Sums, or amalgamations, of two
abelian ordered groups with a subgroup amalgamated are constructed in two ways.
These constructions are used to investigate the structure of the class of all
amalgamations with the given groups and subgroup fixed, where the class is partially
ordered in a natural way. In particular, necessary and sufficient conditions are found
for there to be (a) exactly one amalgamation, up to equivalence, and (b) exactly one
minimal amalgamation, up to equivalence.