class auxiliary
{
    %% Generic class to set constraints between foot and root of aux tree
    Root >>+ Foot;
    node(Root).cat = node(Foot).cat;
    node Root : [id:Root];
    node Foot : [id:Foot];
    node(Foot).type = value(foot);
    node(Root).type = value(std);
    node(Foot).top = node(Foot).bot;
}