static void aPutViewBehindOtherView(final View a, final View b) {
  androidUI(r {
    ViewGroup group = (ViewGroup) a.getParent();
    ViewGroup group2 = (ViewGroup) a.getParent();
    if (group2 != group) ret;
    int i1 = group.indexOfChild(a);
    int i2 = group.indexOfChild(b);
    if (i1 > i2) ret; // order ok
    group.removeView(a);
    group.removeView(b);
    group.addView(b, i1);
    group.addView(a, i2);
  });
}