def atrees_from_doc(ttree_doc, language, selector):
    """Given a Treex document, return a list of a-trees (surface trees)
    in the given language and selector."""
    selectors = selector.split(',')
    atrees = [bundle.get_zone(language, sel).atree
              for bundle in ttree_doc.bundles
              for sel in selectors]
    return atrees