  We give a presentation of various results on zero-groups in o-minimal
structures together with some new observations. In particular we prove that if
G is a definably connected definably compact group in an o-minimal expansion of
a real closed field, then for any maximal definably connected abelian subgroup
T of G, G is the union of the conjugates of T. This can be seen as a
generalization of the classical theorem that a compact connected Lie group is
the union of the conjugates of any of its maximal tori.
