Hi Luca (:+:) is sequential composition - think a melody. (:=:) is parallel composition - think chords. You might find the package - haskore-vintage on Hackage - easier to start with than Henning Thielemann's revised Haskore. Haskore-vintage matches Paul Hudak's original Haskore, which is described in a substantial tutorial. The full Haskore tutorial used to be available from Paul Hudak's home page a Yale - but now that page now seems "under re-construction", a copy is available here: http://www.cs.lth.se/EDA120/assignment2/tutorial.pdf Or PS if you have GhostScript: http://haskell.org/haskore/Haskore/Haskore/Docs/tutorial.ps Or html (though seemingly an older version): http://www.haskell.org/haskore/onlinetutorial/index.html Best wishes Stephen