There used to be two minimal joins between an ordered_set and an abelian_group:

There used to be two minimal joins between an ordered_set and an abelian_group:
ordered_field_ch0 and riesz_space. To avoid the problem without introducing
backtracking in unification I have introduced ordered_abelian_groups.
An ordered_field_ch0 is recast as a field that is also an ordered_abelian_group
and a cotransitively_ordered_set. I still have to recast riesz_spaces as
vector spaces that are also ordered_abelian_groups and lattices.