To the rule “Duel”, add:-

If a duel has only one valid judge and that judge is the King, then the King becomes its judge automatically. If a duel has no opponent and only one valid opponent, and if its judge is the King, and if the post announcing it is more than 48 hours old, then the challenger may make the duel’s valid opponent its opponent by making a comment to that effect on that post, specifying a battlefield of their own choice from among those specified in the post, which becomes the duel’s battlefield.