As per http://developer.android.com/tools/data-binding/guide.html#imports, we can have such simple expressions in visibility:
Thank to everybody, you help me a lot. Your answers were part of my succes on this trouble.
We wanted to set visibility of an image view, that was also target of some animation. The Motion Scene was taking the management of the visibility. Set the motion property app:visibilityMode to "ignore" solve everything.