Add a new subrule to “Cards” called “Trading” as follows:

Should two Wizards, A and B, agree via private communication that Wizard A will trade one card in their hand for one card in Wizard B’s hand, either such Wizard may post a comment (called the “trade announcement comment”) to the GNDT that declares a trade in progress, names the other Wizard, and names the two cards they intend to trade. The other Wizard may then, within 24 hours, perform this trade (with both cards changing hands simultaneously) and update the GNDT to reflect it.

Both cards must still be in their respective Wizards’ hands until the trade is performed, or it cannot take place. If the trade announcement comment is more than 24 hours old, and the trade has not yet been completed, the trade attempt is rendered invalid and must be restarted with a new trade announcement comment if the trade is still to take place.