Hello, While reading the lectures of Luest and Theisen on string theory I encountered the Torelli group. They are very vague about it (the discussion is at pages 118-119) but they say that it correspond to twists arround trivial cycles so the homology basis is unchanged but these transformations are non-trivial diffeomorphisms nevertheless. I searched the Web for some drawing describing these twists but I couldn't find them. Would some kind soul explain them to me? I *think* that they should be like the Dehn twists but I'm not sure about that. There's some other interesting piece of information in Luest & Theisen about the moduli space of genus g Riemann surfaces. It seems that this moduli space gets quite complicated for genus g > 3. I think g=3 is the state of the art in computing superstring amplitudes (I have no idea about bosonic string amplitudes). I therefore think it's necessary to go at least to g=4 to see if there's something qualitatively different there.