hi cyrille, I was playing around with some collisions and found a strange behaviour which looks buggy to me. I was shooting a sqare against a circle and at some points the rebound went to strange directions. I tried to make a debug patch to show this behaviour (circle_testpmp.pd) you will also need the other abstraction to run it. If someone else wants to look at it, please do! thanks for any help, or corrections. (btw. I also found this strange behaviour with rebounds from lines, so maybe it is not a bug, but I am just doin something wrong). marius.