DescriptionThis Event Outcome will Settle to "Yes" if a credible reporting source confirms that the Mayor of London or the Greater London Authority files a legal challenge or joins a lawsuit against the Heathrow third runway project before the Event Date Close. If it becomes impossible for this Event Outcome to Settle to "Yes", the Event Outcome may Settle immediately to "No". The primary source for this Event Outcome will be legal filings, mayoral office statements, or a consensus of credible political and environmental reporting sources. The Event Outcome is a Prediction on an Announcement from a credible reporting source.