walter vromans was an assistant at which football match that has a start date that is less than or equal to 2010-06-29t16:00:00-08:00?
(AND soccer.football_match (AND (JOIN (R soccer.football_referee.assistant_referee_at) m.0c0mfbj) (le time.event.start_date 2010-06-29T16:00:00-08:00^^http://www.w3.org/2001/XMLSchema#dateTime)))