// FIXME
for(Sequence ss : s.needs()) ret = union((Union)e, ret, walk(ss));
for(Sequence ss : s.hates()) ret = union((Union)e, ret, walk(ss));
// FIXME
for(Sequence ss : s.needs()) ret = union((Union)e, ret, walk(ss));
for(Sequence ss : s.hates()) ret = union((Union)e, ret, walk(ss));