Dora Giammarresi Jean-Luc Ponty Derick Wood Djelloul Ziadi A characterization of Thompson digraphs. 317-337 2004 134 Discrete Applied Mathematics 1-3 http://dx.doi.org/10.1016/S0166-218X(03)00299-3 db/journals/dam/dam134.html#GiammarresiPWZ04