able_item,[triggered(Valuable_item),protected_by(Valuable_item,Trigger)])],
    % necessary
    [     sc(system,System,[active(System)]=>[emergency(System)])],
    % conditional
    []).
operator(alert(System,Guard),
    % prevail
    [     se(system,System,[emergency(System)])],
    % necessary
    [     sc(guard,Guard,[working(Guard,System)]=>[alerted(Guard,System)])],
    % conditional
    []).
operator(back_to_work(Guard,System),
    % prevail
    [],
    % necessary
    [     sc(guard,Guard,[alerted(Gu