On the height of subgroups of Homeo(I)
  In [Bl1], it is proved that a subgroup of $PL_{+}(I)$ has a finite height if and only if it is solvable. We prove the "only if" part for any subgroup of Homeo$_{+}(I)$, and present a construction which indicates a plethora of examples of solvable groups with infinite height. 
Azer Akhmedov
math.GR math.DS