Thanks for answering.
It could works using expressions,
but the problem is : the PRECOMP is bigger than COMP, and i use keyframe to animate PRECOMP… so then,the layer CLIP doesn’t perfectly follow the layer DISK anymore…
In fact it works if I use expressions, and if I link CLIP to PRECOMP… It is not very handly I think, because I loose some control on CLIP (can’t change the scale etc…)