Reversibility in the groups of PL^+(S^1) and PL(S^1)
  Let PL+(S1) be the group of order preserving piecewise linear homeomorphisms of the circle. An element in PL+(S1) is called reversible in PL+(S1) if it is conjugate to its inverse in PL+(S1). We characterize the reversible elements in PL+(S1). We also perform a sim- ilar characterisation in the full group PL(S1) of piecewise linear home- omorphisms of the circle. 
Khadija Ben Rejeb and Habib Marzougui
math.GR